[settings] - implement update mechanism for audiooutput setting (needed due to new setting format)
Revert "[osx] drop outputbuffer index and iterate over them all"

This reverts commit b9a1d07a7d1a2bec3bb094b97cc7d96a325b9b98.

Conflicts:
	xbmc/cores/AudioEngine/Sinks/AESinkDARWINOSX.cpp
[osx/coreaudio] - add methods for fetching audio sources and their names
[osx/coreaudio] - add method for fetching the the start channel number of a stream in relation to its owner device
[AE/osxsink] - display the current source name as device extra info
[AE/osxsink] - add pseudo devices for devices with multiple non-planar streams - and obey the streamidx during initialize/streamscoring
[osx/coreaudio] - add method for setting the audio source of a device
[AE/osxsink] - enumerate the audio sources of a device if there are any - this allows to select between multiple airplay sinks for example
fixups