Subtitle queue: Ensure the queue is invalidated after seeking.

Fixes #3691.
Subtitle queue: Check the invalidation time against the segment end time.

We could miss some subtitles which needed to be invalidated.

Fixes #3691.
PGS Subtitles: Correctly reset the parser after seeking.

Subtitles displayed just after seeking could be wrong.
PGS Subtitles: Ensure the bounding box is correct when the subtitle isn't rendered.

This could cause a black flash if a subtitle failed to render (after seeking for example).

Fixes #3691.
Cosmetic: Remove an unused function.

This was forgotten during a re-factoring long ago.
CompositionObject: Delete the assignment operator for now.

Forbid the use of direct affectation for now, it would be dangerous because of possible leaks and double frees. We could do a deep copy to be safe but it could possibly hurt the performance if we forgot about this and start using affectation a lot.
Update mhook link.
contrib/rev2hash.sh: remove unused variable.
WebUI: refactor and clean up javascript code.
WebUI: add title in the player's buttons.
WebUI: rename functions and enable strict mode.
WebUI: refactor and tweak styles.
WebUI: switch to `link rel="icon"`.
WebUI: Use a cleaner favicon.ico.
WebUI: show a warning in player.html too if JS is disabled.
WebUI: clean up the `noscript` code.
WebUI: show a warning for IE < 8.

Things don't look good there for some time now.  IE8+ works fine.
WebUI: Add title with the volume level to the volume grip.
Update ZenLib to v0.4.29 r446.
Update MediaInfoLib to v0.7.68.