libtroc-video: Clear overlays in VideoPlayer::Reset
libtorc-video: Extend/fix TorcVideoOverlay

- increase the max queue size
- differentiate between timed and non-timed, menu overlays. Bluray menu
overlays do not have a pts - they are expected to be presented as soon
as they are delivered.
- add support for bluray overlay buffers
- track the stream index for AVSubtitles. NB this is the index into
Torc's subtitle stream descriptors, not the raw AvFormatContext stream
list.