GLMixer Code

Updated support to ShadeToy; switched to iTime variable (deprecated
iGlobalTime) and added informative warnings about syntax changes.

Bug Fix: idem previous, but cleaner implementation.

Bug Fix: correct management of picture queue on changes of marks for
begin and end (clean_until_time_picture_queue)

Fixed GUI: disabling / enabling timeline according to source type and
status.

Bug Fix : clamp rotation angles of source in range [0..360] (not a real
issue for rendering, just for display of angle property.

Bug Fix; hide the link between sources of same group in mixing view when
exclusive workspace mode is on.

Bug Fix : clamp rotation angles of source in range [0..360] (not a real
issue for rendering, just for display of angle property.

Bug Fix: crash after replacing a source.

Improved dialog for source edit (add plugin browser when useful).

BUG Fix in previous fix.