[rbp/omxplayer] Support both analogue and hdmi audio

Thanks to stupid-boy for original implementation.
[OverlayRenderGL] Fix corrupt pixels in graphical subs

On Pi you can see a corrupt line of pixels on bottom and right edges of subtitle bounding box.
This is due to using a subregion of a texture (due to the power of two rounding) and not ensuring
the texture coordinates are inside the valid pixels.

The easy solution is to use NPOT when available (always on GLES) and then the clamping works
(as well as saving memory).
[rbp/omxplayer] Cosmetics
[rbp/omxplayer] Improve the player diagnostics overlay
[rbp/omxplayer] Avoid too many calls to GPU

We currently read the media time once per packet received from demuxer to determine gpu underrun.
We've found that TrueHD audio in particular produces ~1000 packets per second (whether it is the active track or not).
The cost of reading media time (from gpu) is high enough that 1000 calls per second makes us fail to keep up.
So, cache the media time, and only read it at most 50 times per second.