Adds dashboard Department CRUD and simple Cancan perms.

Admins with a role of project_manager are now able to CRUD
Departments. Admins with a role of ticket_moderator are restricted
to CRUD on the Ticket resource. The Cancan gem powers the perms
system.
Adds dashboard Priority CRUD.

Admins with a role of project_manager can now CRUD Priority resources.
This is about as bare-bones as it can get at the moment, but is a
starting point for better things. The next step for Priorities will be
to add an explicit rank order to them as well as some UI tools for
prioritizing the priorities.
Adds Priority ordering.

Admins with a role of project_manager are now able to organize
priorities by order. This allows for a meaningful arrangement
of priorities when presenting them to the User (rather than just
according to creation order).