Store list of channels displaying in dopesheet separately from list of tracks.
This allows to re-sort channels in dopesheet independently from list of all
tracks (currently only alphabetic sorting is implemented).
This also allows to cache assorted information (like tracked segments of track)
but currently such a things are not bottlenecks and could be done after merge
dopesheet view into trunk.
TODO:
- Still have some deadlocks when drawing selected channels.
Skipping channel background or keyframe drawing helps here but
this need to be resolved.
- Bump sub-version and wrote code needed to convert pre-dopesheet interface
with opened curve view displaying properly.
- Probably it'll worth caching tracked segments.
ebe4ffa8de