Permissions update

Old access level mechanism was not very elegant. This replaces how permissions are handled with a more extensible method of handling permissions. Also provides a method to manually assign someone permissions without worrying about house positions.

Database changes:
- New table `office_permissions`
- New table `user_permissions`
- Will remove `access_level` from `offices`
Fixed this in 5d05ae. I didn't mean for every permission to be admin - I just forgot to use the `Permissions.Admin` permission I introduced in a previous commit.