Fix DVB and PGS subtitles after 733bc17aaed8751565c5343c9b0e7ecce96c2796.

The timings were wrong after the first seek.

Simplify the code to use real timing for all subtitle types.
DVB subtitles: Try to make some sense out of the PTS parsing code.

Also fix a typo which had no effect on the execution and remove member variables that were used only in one function.

Fixes CID 1233585.
Don't force any background color for the Shockwave graph.

This commit fixes #1747.
Why "C:\tmp.srt"?
WebUI: Inform the web interface that no audio stream is available.
WebUI: Make use of new [hasaudio] info.
What the hell was intended here?!

Trying to make some sense of that code. Without much luck so far...