This adds support for displaying subtitles embedded in movie files. This
supports files with multiple subtitle streams where each stream contains
the subtitles for one language. When the movie file is opened, the
stream for the currently active language will be used and displayed.
This resolves one of the points mentioned in #1522.
This also depends on PR #1484.
It turns out that FFmpeg is actually able to decode the Interplay MVE
movies so we can drop the old MVE code and just use FFMpeg and the new
video player interface for that.
David Carlier