Remove APIs:
ges_track_element_set_locked
ges_track_element_is_locked
Those APIs where really not nice to use and were causing more issues
than solving them. If 2 time related properties of TimelineElement must
be different, then those element can *not* have the same parent.
Plus, with the new ges_container_group () API, we will recreate 1
GESClip containing the proper GESTimelineElements if it is the thing
to do.
... Not the other way round.
+ Add and enhance debugging info on the way
The user should not be responsible for removing the GESTrackElements from
GESTracks, instead, removing it from a GESClip should imply removing
it from any GESTrack it is in.
This patch changes sensibly the behaviour when we remove a
GESTrackElement from a GESTrack, not remoing it from the GESClip it is
in. *But*, users should never remove a GESTrackElement from a GESTrack
anyway. The testsuite has been updated to that new behaviour.