game_engine. Change audio source creation in game engine.

Change the audio source creation method in game engine to return a pointer to the created audio source.
game_engine. Add error handling in engine event methods.

Catch java exceptions thrown from native layer in the engine on<some_event> methods.
Throw an audio operation error method in on touch.
game_engine. Fix to JNI interface error handling.

Add a utility method to check if a Java exception is pending.
Return immediately from all JNI calls if a Java exception is pending.
Fix to java exception names thrown from native code.