MacGui: Audio ... Allow more than 4 audio tracks.

MacGui: Audio ... Allow more than 4 audio tracks.
- Patch courtesy of circleone ...  Thanks!
- Use a NSTableView to dynamically add/delete audio tracks ala the Subtitle tab.
- Sets a 24 track limit until someone tests more than 24 tracks (the libhb 8 track limit was removed as per http://trac.handbrake.fr/changeset/3531).
- Replaces the old static 4 tracks to a dynamic array.
- Moves macgui audio handling to a separate class.
Known caveats:
- Borks queue editing which needs a revamp anyway.
- Queue window display needs to be adjusted to show more than 4 tracks appropriately. Again, its cosmetic and is not a show stopper.
- There may be other possible unknown side effects even though tested on all presets. That said, I feel it needs to get in so that we can get feedback from nightlies.

git-svn-id: svn://localhost/HandBrake/trunk@3532 b64f7644-9d1e-0410-96f1-a4d463321fa5