KUbuntu 14.04 support restored (#1298)

* - [NEW] Add new interface and functionality to manage database file extension. (Implements feature request #659)

* - [FIX] Fixed CMake file to src.pro

* - Applied changes requested by mgrojo to uniform code with sqlitebrowser standards
- Add "history" when closing editor window, but reopen before closing preferences
- Revert some changes done by QtCreator

* Refuse from previous commit

* Additional changes requested by MKleusberg:
- [CHG] Always add "All files (*)" to filters
- [FIX] Removed unused include

* merged from master

* Merge sqlitebrowser master

* [FIX] Fixed compatibility to compile on KUbuntu 14.04 with Qt 5.2.1

* [FIX] Fix Qt version for QOpenGLWidget support on previous commit

* [CHG] Uniformed QT_VERSION_CHECK style
[CHG] Reverted macOS check on Mainwindow for OpenGL context creation

src/MainWindow.cpp

@@ -48,9 +48,12 @@
 #include <QClipboard>
 #include <QShortcut>
 #include <QTextCodec>
-#include <QOpenGLWidget>
 #include <QUrlQuery>
 
+#ifdef Q_OS_MACX //Needed only on macOS
+    #include <QOpenGLWidget>
+#endif
+
 MainWindow::MainWindow(QWidget* parent)
     : QMainWindow(parent),
       ui(new Ui::MainWindow),
@@ -84,8 +87,8 @@ void MainWindow::init()
     tabifyDockWidget(ui->dockLog, ui->dockSchema);
     tabifyDockWidget(ui->dockLog, ui->dockRemote);
 
-    // Add OpenGL Context for macOS
 #ifdef Q_OS_MACX
+    // Add OpenGL Context for macOS
     QOpenGLWidget *ogl = new QOpenGLWidget(this);
     ui->horizontalLayout->addWidget(ogl);
     ogl->setHidden(true);