Feature 42 - Adding assignees to tasks

- updated view panel UI
- changed Tasks to store String usernames instead of User objects (caused user duplication bug)
- added controllers to retrieve users from the database
- created logic for switching users in the create/edit panels
- other minor supporting changes

Manual tests not yet written; I will let you know once those are done.

Thanks!

@set15 @pluxsuwong @johnn134