[cmyth] Internal EDL

- Adding cmyth_mysql_get_recording_seek_offset(): Return offset for mark of frame
[mythtv-cmyth] Internal EDL

- Playback with internal EDL (read and seek forward) based on positions of frame headers around the marks.
- On skip back then ignore handled cut. (But once passed, don't ignore it anymore)
- Add ADDON setting edl_method_provider (PVR | Internal). Default is PVR.