Issues that need to be fixed for ~~17.12~~ Refactoring release:
[x] copy / paste clips
[ ] project duration
[ ] composition : move a_track correctly
[x] geometry keyframes (transform,etc)
[ ] slowmotion effect - in progress
[x] fix adding clip in bin (corruption with color clip id because of unfinished porting to new method)
[x] split audio
[x] define target track (audio/video) for operations
[x] Clicking away (eg at an empty place of the timeline) should clear clip selection
[ ] Allow compositions in groups
[ ] Copy/paste compositions
[ ] Insert several clips
[x] Track effects
[x] Track addition/deletion
[] Bin corruption