Incuna-groups

- Added new manager methods for accessing groups, discussions, comments and users.
- Added an `AppConfig` in apps.py for ease of configuration.
- Added new manager methods to return recent groups, discussions, and comments.
- Added a mixin that can be added to User managers or querysets to return recent users.

- Added `comment.render` to the `Comment` model.
- Simplified the comment related templates.

- Add permalinks to comments.
- Comments can now be deleted by the users that made them or admin users.
- Add file comments, allowing users to upload files to discussions.

- Implement the ability to subscribe to discussions.
- Add back links to multiple templates.
- De-require `django` again (to test this locally, you'll need to install it manually).

- Fix a deployment bug by adding `MANIFEST.in`.
- Add a missing requirement for `django`.

- Initial release.