[AE/osxsink] - fix multichannel speaker layout / channel mapping

This finally makes the osxsink usable with lpcm (multichannel pcm). This might also close some trac tickets (wrong channel mapping, maybe the audio sync issue which iirc only is a problem on passthrough).

I tested all scenarios i could think of with my pretty common hdmi 5.1 receiver. I have documented the tests here:

http://pastebin.com/anFA9QH4

It would be great if someone with a 7.1 setup can verify that 7.0 and 7.1 works fine aswell. @jmarshallnz iirc you have at least a 5.1 setup aswell. Maybe you find some time to confirm my test results (the 5.1 audio test file is linked in the pastbin aswell).

This only handles interleaved audio. Not sure how this should be done for planar.

This should be gotham material as it is a big step for completing the osx sink.