* similar to http://www.vatsim.net/fp/
* own form, own widget class as a trial to further modularize GUI components
* removed all view models (now encapsulated)
* tweaked style sheet
* prepared for login/off sounds
* prepared for text message sounds
* helper method to play sounds
* enabled mute / mixer also in cockpit, including context menus
* settings for notification sounds
* some minor tweaks, e.g. changed signal/slot to C++ style where missing