Adjust clip start and end

[owickstrom]

When importing an asset into the library, the asset data structure describes the start and end timestamps of the original video file. If you import without automatic classification, those will be the start and end times of the entire video, i.e. the whole video. When you do use automatic classification (with the exception for audio, currently!) the timestamps will be the start and end of each classified scene.

When adding one of these assets as a clip in the timeline, you get whatever start and end timestamps for the clip as they were in the library. It would be nice if you could adjust the clip start and end, for instance if the classified scene was a bit off, or if you need to hand-edit for some other reason.

In a traditional editor this would be the "drag to adjust" borders on the clip box, but I'm not sure about how it should work in Komposition. Maybe an "edit" command, such that if you press "e" when focusing a clip, you'll get a dialog where you can adjust these values. Or something like a "nudge start" and "nudge end", so that you don't need the intermediate dialog.

[owickstrom]

Fixed by #68