Add system tray icon option (all systems) and dbus support (X11 systems only)

Add system tray icon (optionnal: must be checked on settings) with personnal menu
- Lock database
- Close database
- Show/Hide application
- Quit

If system tray icon is enabled, close action (by 'X' window manager) is replace by hide, but quit action on menu is still a quit action.

Add DBus support on X11 system (compilation time: ifdef Q_WS_X11).