[rbp] Add support for gui sounds to PiAudio backend
[rbp/omxplayer] Fix for subtitle flood at start of file

The test for pts==0 results in every subtitle in the overlay container being rendered at start of file.
#2565 results in every subitle from an external file being loaded into the overlay container at start of file.

This results in hundreds of subtitles being rendered which is slow and ugly. See:
https://dl.dropboxusercontent.com/u/3669512/temp/screenshot001.png

Remove this test.

Also remove setting the media_pts to the predicted media_pts as that causes a subtitle flurry after seeking while GPU fifo fills
[rbp] Ensure resolution infos have unique names

Currently the strMode for 2D and 3D resolutions have the same name.
This means the calibration info for a 2D mode can get replaced with a 3D mode
which can result in the pixel aspect ratio being reset to 0.5.

Also when using gui resolution clamping (i.e. 720p gui on 1080p display)
the calibration settings are scaled to gui resolution, but there is no indictation
of what the clamped resolution was when the settings were saved.

This means disabling gui clamping results in a minature gui.

Make sure all these resolutions have unique names by adding the gui resolution
and 3DSBS/3DTB to the resolution string.
fix issues with iOS 7 AirPlay streaming
[rbp/omxplayer] Handle mono playback of HSBS/HTAB videos