A lot of fixes for anim_startofs / anim_endofs:
* crashed when striplen was 0 and startstill / endstill still in use
* made it work for Audio (HD and RAM)
* made it work for Image Sequences
* added a new cutting tool, that uses anim_startofs / endofs instead of
startofs / endofs. This is now the default and called "hard cut"
* moved old cutting method to "Shift-K" and renamed it "soft cut"
8d2a0a566f