Logic was broken into finding gaps and ofsetting strips.
Functions were modified so they work on explicitly defined seqbase,
so they can be used as python API functions.
Functional changes:
- Improve performance by calculating gap length and offseting strips
at once. Previously strips were offset by one frame.
- Calculate gap from start frame. Previously gap was considered only
inbetween strips.
Reviewed By: sergey
Differential Revision: https://developer.blender.org/D9730
Move most functions into separate files.
File sequencer.c is reserved for alloc, free and duplicating functions.
There should be no functional changes.
