Add "clear track" option, fix copying of tracks from song ed -> bb ed
- Tracks copied from song->bb will no longer be unusable
- Since doing this required creating a "delete TCOs from track" function, I also added the option to trackops menu to clear a track
Fix #757
Merge pull request #1005 from diizy/stable-1.1

Add "clear track" option, fix copying of tracks from song ed -> bb ed