extra layer drag and drop option.

[Peter Wassink]

Today during a TVPintroduction class, i realized i missed an option in dragging frames.
when moving a selection of frames in a layer, you get the option menu asking:
- copy
- move
- insert

Each have their use, but i was missing the option to insert without copy.
in other words i want an option 4 : - insert + move

so we get:
- copy
- move
- insert a move
- insert a copy

[schwarzgrau]

Yea, I noticed the same a few days ago. I thought it would be my mistake, since I didn't used this function a lot.