Add ability to import media from a local directory

And, there it is!

Very rough. Tried to import dirs, etc. Perhaps file_scan_dir is a better option. I was eyeing the simplest solution. We'll certainly want to add support for FTP, S3 and HTTP imports, and import w/o copy.

Anyway, it's a start, and quite fun to play with (plus it lets me test the dynamic scroller and filters better).