Add option to lock databases after user inactivity.

Closes #62

src/gui/MainWindow.h

@@ -28,6 +28,8 @@ namespace Ui {
     class MainWindow;
 }
 
+class InactivityTimer;
+
 class MainWindow : public QMainWindow
 {
     Q_OBJECT
@@ -58,6 +60,7 @@ private Q_SLOTS:
     void showGroupContextMenu(const QPoint& globalPos);
     void saveToolbarState(bool value);
     void rememberOpenDatabases(const QString& filePath);
+    void applySettingsChanges();
 
 private:
     static void setShortcut(QAction* action, QKeySequence::StandardKey standard, int fallback = 0);
@@ -70,6 +73,7 @@ private:
     QActionGroup* m_lastDatabasesActions;
     QActionGroup* m_copyAdditionalAttributeActions;
     QStringList m_openDatabases;
+    InactivityTimer* m_inactivityTimer;
 
     Q_DISABLE_COPY(MainWindow)
 };