Updating admin interface

- Renamed ViewRequiresAuthorization to SecureMixin
- Added FileView for uploads and downloads
- Added categories
- Updated tests
- Updated dependnecies to use git.master for Flask-Admin as 1.0.6 is
  incompatible with Flask-WTF >= 0.9 (This will cause issues in prod)
Renaming admin tests
Fixing pep8 issues in tests