Added slug field to model
Changed instances of file.pk to file.slug and file_id to slug
Used slug for url rather than primary key
Changed all instances of file.pk to file.slug
Changed all instances of group.pk to group.slug
got rid of obfuscation filters
Fixed some bugs created by going from pk -> slug
Implemented updated django-perms package to take care of broken permissions
Fixed some tests
Fixed tests
Merge pull request #1 from kfarr2/slugs

Now working with slugs rather than primary keys