Refactor TrackContainer method names (remove "Track" from end)
Implement TrackContainer.getById

Inner implementation of TrackContainer was changed to use LinkedHashMap
instead of HashMap, so insertion order is preserved and tracks can be
fetched by their indexes.
Rename Track.insertKey -> addOrUpdateKey and change logic
Implement Track.deleteKey
Bugfix: correctly update Track's value also for row 0
Refactor keyframe lookup into separate method