SVN commit 628921 by metz:

- Pull state management into EngineInterface instead of guessing the engine-state in Player class
- Add error reporting to EngineInterface and Player
- Finally fix broken apidocs for NMainWindow, forgot @endcode
- Adapt akode-backend to new EngineInterface


 M  +15 -14    library/noatun/nmainwindow.h  
 M  +96 -37    library/noatun/player.h  
 M  +53 -29    library/noatun/plugininterfaces.h  
 M  +42 -35    library/player.cpp  
 M  +15 -12    library/plugininterfaces.cpp  
 M  +64 -45    modules/akode-engine/noatun_akode.cpp  
 M  +9 -10     modules/akode-engine/noatun_akode.h