Set Config- and Data-Directory to system-specific paths

diff --git a/sources/dxf/dxftoelmt.cpp b/sources/dxf/dxftoelmt.cpp
index f2dd572d8..85ea2534f 100644
--- a/sources/dxf/dxftoelmt.cpp
+++ b/sources/dxf/dxftoelmt.cpp
@@ -21,7 +21,7 @@
 #include <QFile>
 #include <QProcess>
 #include <QMessageBox>
-#include <QDir>
+#include <QStandardPaths>
 
 /**
  * @brief dxftoElmt
@@ -71,13 +71,7 @@ QByteArray dxfToElmt(const QString &file_path)
 
 QString dxf2ElmtDirPath()
 {
-#if defined(Q_OS_WIN32) || defined(Q_OS_WIN64)
-    return (QDir::homePath() + QStringLiteral("/Application Data/qet/binary"));
-#elif defined(Q_OS_MACOS)
-    return (QDir::homePath() + QStringLiteral("/.qet/binary"));
-#else
-    return (QDir::homePath() + QStringLiteral("/.qet/binary"));
-#endif
+    return QStandardPaths::writableLocation(QStandardPaths::AppDataLocation) + "/binary";
 }
 
 /**
diff --git a/sources/main.cpp b/sources/main.cpp
index ed460609f..5eb7efca3 100644
--- a/sources/main.cpp
+++ b/sources/main.cpp
@@ -112,7 +112,8 @@ void myMessageOutput(QtMsgType type,
         txt+= context.function ? context.function : "";
         txt+=")\n";
     }
-    QFile outFile(QETApp::configDir()
+    QFile outFile(QETApp::dataDir()
+              +"/"
               +QDate::currentDate().toString("yyyyMMdd")
               +".log");
     if(outFile.open(QIODevice::WriteOnly | QIODevice::Append))
@@ -131,7 +132,7 @@ void myMessageOutput(QtMsgType type,
 void delete_old_log_files(int days)
 {
     const QDate today = QDate::currentDate();
-    const QString path = QETApp::configDir() + "/";
+    const QString path = QETApp::dataDir() + "/";
 
     QString filter("%1%1%1%1%1%1%1%1.log"); // pattern
     filter = filter.arg("[0123456789]"); // valid characters
diff --git a/sources/qet_elementscaler/qet_elementscaler.cpp b/sources/qet_elementscaler/qet_elementscaler.cpp
index 930bae333..b7e362d1e 100644
--- a/sources/qet_elementscaler/qet_elementscaler.cpp
+++ b/sources/qet_elementscaler/qet_elementscaler.cpp
@@ -22,7 +22,7 @@
 #include <QProcess>
 #include <QInputDialog>
 #include <QMessageBox>
-#include <QDir>
+#include <QStandardPaths>
 
 /**
  * @brief QET_ElementScaler
@@ -113,13 +113,7 @@ QByteArray ElementScaler(const QString &file_path, QWidget *parent)
 
 QString ElementScalerDirPath()
 {
-#if defined(Q_OS_WIN32) || defined(Q_OS_WIN64)
-    return (QDir::homePath() + QStringLiteral("/Application Data/qet/binary"));
-#elif defined(Q_OS_MACOS)
-    return (QDir::homePath() + QStringLiteral("/.qet/binary"));
-#else
-    return (QDir::homePath() + QStringLiteral("/.qet/binary"));
-#endif
+    return QStandardPaths::writableLocation(QStandardPaths::AppDataLocation) + "/binary";
 }
 
 /**
diff --git a/sources/qetapp.cpp b/sources/qetapp.cpp
index f1211bb47..e7611fd88 100644
--- a/sources/qetapp.cpp
+++ b/sources/qetapp.cpp
@@ -121,7 +121,7 @@ QETApp::QETApp() :
         tr("Chargement... Initialisation du cache des collections d'éléments",
            "splash screen caption"));
     if (!collections_cache_) {
-    QString cache_path = QETApp::configDir() + "/elements_cache.sqlite";
+    QString cache_path = QETApp::dataDir() + "/elements_cache.sqlite";
 
         collections_cache_ = new ElementsCollectionCache(cache_path, this);
         collections_cache_->setLocale(langFromSetting());
@@ -620,7 +620,7 @@ QString QETApp::customElementsDir()
             }
         }
 
-        m_custom_element_dir = configDir() + "elements/";
+        m_custom_element_dir = dataDir() + "/elements/";
         return m_custom_element_dir;
     }
 }
@@ -657,7 +657,7 @@ QString QETApp::companyElementsDir()
             }
         }
 
-        m_company_element_dir = configDir() + "elements-company/";
+        m_company_element_dir = dataDir() + "/elements-company/";
         return m_company_element_dir;
     }
 }
@@ -780,7 +780,7 @@ QString QETApp::companyTitleBlockTemplatesDir()
         return m_user_company_tbt_dir;
     }
 
-    return(configDir() + "titleblocks-company/");
+    return(dataDir() + "/titleblocks-company/");
 }
 
 /**
@@ -813,7 +813,7 @@ QString QETApp::customTitleBlockTemplatesDir()
         return m_user_custom_tbt_dir;
     }
 
-    return(configDir() + "titleblocks/");
+    return(dataDir() + "/titleblocks/");
 }
 
 /**
@@ -841,21 +841,31 @@ QString QETApp::configDir()
 #ifdef QET_ALLOW_OVERRIDE_CD_OPTION
     if (config_dir != QString()) return(config_dir);
 #endif
-#ifdef Q_OS_WIN32
-    // recupere l'emplacement du dossier Application Data
-    // char *app_data_env = getenv("APPDATA");
-    // QString app_data_str(app_data_env);
-    QProcess * process = new QProcess();
-    QString app_data_str = (process->processEnvironment()).value("APPDATA");
-    // delete app_data_env;
-    delete process;
-    if (app_data_str.isEmpty()) {
-        app_data_str = QDir::homePath() + "/Application Data";
-    }
-    return(app_data_str + "/qet/");
-#else
-    return(QDir::homePath() + "/.qet/");
-#endif
+    QString configdir = QStandardPaths::writableLocation(QStandardPaths::AppConfigLocation);
+    if (configdir.endsWith('/')) {
+        configdir.remove(configdir.length()-1, 1);
+    }
+    return configdir;
+}
+
+/**
+    @brief QETApp::dataDir
+    Return the QET data folder, i.e. the path to the folder in which
+    QET will find user-collections and user-titleblocks by default
+    specific to the current user. This directory is generally
+    C:/Users/<USER>/AppData/Roaming/<APPNAME>
+    on Windows and
+    ~/.local/share/<APPNAME>
+    under UNIX-like systems.
+    \~ @return The path of the QElectroTech data-folder
+*/
+QString QETApp::dataDir()
+{
+    QString datadir = QStandardPaths::writableLocation(QStandardPaths::AppDataLocation);
+    if (datadir.endsWith('/')) {
+        datadir.remove(datadir.length()-1, 1);
+    }
+    return datadir;
 }
 
 /**
@@ -1536,7 +1546,7 @@ void QETApp::useSystemPalette(bool use) {
                 "}"
                 );
     } else {
-        QFile file(configDir() + "style.css");
+        QFile file(configDir() + "/style.css");
         file.open(QFile::ReadOnly);
         QString styleSheet = QLatin1String(file.readAll());
         qApp->setStyleSheet(styleSheet);
diff --git a/sources/qetapp.h b/sources/qetapp.h
index 2f4cdc402..572e2c837 100644
--- a/sources/qetapp.h
+++ b/sources/qetapp.h
@@ -97,6 +97,7 @@ class QETApp : public QObject
         static QETProject *project(const uint &);
         static int projectId(const QETProject *);
         static QString configDir();
+        static QString dataDir();
         static QString languagesPath();
         static QString realPath(const QString &);
         static QString symbolicPath(const QString &);
diff --git a/sources/ui/aboutqetdialog.cpp b/sources/ui/aboutqetdialog.cpp
index b1dc0abc0..f94b62449 100644
--- a/sources/ui/aboutqetdialog.cpp
+++ b/sources/ui/aboutqetdialog.cpp
@@ -208,7 +208,7 @@ void AboutQETDialog::setLicence()
 */
 void AboutQETDialog::setLoginfo()
 {
-    const QString path = QETApp::configDir() + "/";
+    const QString path = QETApp::dataDir() + "/";
     QString filter("%1%1%1%1%1%1%1%1.log"); // pattern
     filter = filter.arg("[0123456789]"); // valid characters
     Q_FOREACH (auto fileInfo,