fixes to EDL import

- allow editmode 'a1', 'a2', 'a3'... etc
- allow editmode 'none'
- accept black as 'bl', 'bw', 'blk', 'black'
- black was being imported as grey
- add global frame offset option for importing
- fix error naming strips
- if a reel has an extension, match with the extension stripped as well --- so foobar.mov will find foobar.avi file.