Tweaks to plane track

- Do plane re-evaluation only when transform is actually done.
  Before this re-evaluation happened on every mouse move.

- Added a flag "Auto Keyframe" for the plane track, which does:

  * If Auto Keyframe is enabled, then every manual edit of the
    plane will create a new keyframe at current frame and update
    plane motion between current frame and previous/next keyframe.

    This now also implies blending detected motion with neighbor
    keyframes, so there's no jump happening.

    No automatic update on manual point tracks edit will happen.

  * If auto Keyframe is disabled, then no keyframes are adding
    to the plane and every plane tweak will re-evaluate in on
    the whole frame range.

    In this case manual tweaks to point tracks and re-tracking
    them implies plane re-evaluation.

source/blender/editors/transform/transform_generics.c

@@ -659,9 +659,7 @@ static void recalcData_spaceclip(TransInfo *t)
 	if (ED_space_clip_check_show_trackedit(sc)) {
 		MovieClip *clip = ED_space_clip_get_clip(sc);
 		ListBase *tracksbase = BKE_tracking_get_active_tracks(&clip->tracking);
-		ListBase *plane_tracks_base = BKE_tracking_get_active_plane_tracks(&clip->tracking);
 		MovieTrackingTrack *track;
-		MovieTrackingPlaneTrack *plane_track;
 		int framenr = ED_space_clip_get_clip_frame_number(sc);
 
 		flushTransTracking(t);
@@ -692,15 +690,6 @@ static void recalcData_spaceclip(TransInfo *t)
 			track = track->next;
 		}
 
-		for (plane_track = plane_tracks_base->first;
-		     plane_track;
-		     plane_track = plane_track->next)
-		{
-			if (plane_track->flag & SELECT) {
-				BKE_tracking_track_plane_from_existing_motion(plane_track, framenr);
-			}
-		}
-
 		DAG_id_tag_update(&clip->id, 0);
 	}
 	else if (t->options & CTX_MASK) {