[audio transitions] Fix porting error (acontrolsource != bcontrolsource), call duration_changed at creation and update debug statements.²
Update test_audio_transition
In project, when id is NULL use the name of the extractable_type
Add a resampler in the audio transition bin
asynchronously add bindings if the track-element is not in a track yet.

Also fix annotations.
Add the stem of a test  for video transitions.
replace query_caps with get_current_caps. don't check for unused gnlobject.