#2059 - Add album name sanitizing similar to photo/movie filename sanitizing.
- added legal_file::sanitize_dirname(), analogous to sanitize_filename.
- revised item model to use new function when adding or updating an album.
- added some legal_file unit tests.
- revised some item model unit tests.
Merge pull request #214 from shadlaws/fix_2059

#2059 - Add album name sanitizing similar to photo/movie filename sanitizing