In #85 the voice context will be renamed to audio context, so the CValueObject classes will be renamed to namespace Audio too.
As #140 changes many CValueClasses, this crossover change is done in the same unit of work.
* 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
* added methods to get results in context
* added signal to indicate audio test completed
* updated GUI to display results
* changed test run methods to non-const to be consistent with voice lib
* Logic in GUI to avoid parallel / interfering tests
* Fixed wrong Q_ASSERT message and QTimer::singleShot in voice_vatlib.cpp
Some minor changes in the same step:
* Fixed some style sheets
* Added QToolBox as preparation for a status message list
* Renamed voice settings to audio settings
