Testing and bug fixes

Small improvements to sort-photos.sh
Verify rsync is installed
Some other things
Video sorting bug fixes.
Use more consistent variable names
Add a prompt before reviewing videos
Tested and fixed video sorting
Fix --mount-point directory verification in import-photos
Allow use of root for mounting devices

Use a the current user's uid/gid and a sensible umask
Implemented safe_copy

Copies files and automatically renames if the file exists while
preserving the extension.
Implemented safe_flatten
Move import-only functions out of common
Quote all the files.

And some other bug fixes
Added README and LICENSE
Use local variables in functions
Added a test script for import-photos.sh