Post-MVP for adding, editing, deleting departments

### As an administrator, I want to be able to add, edit, and delete departments, so that I can have control over the permissions model.

- [ ] For each listing:
- [ ] Indicate number of users assigned to a department
- [ ] Last login includes username with login timestamp
- [ ] A user can only delete if there are 0 users in the department
- [ ] If an administrator clicks the "delete" button and there are 1 or more users in that department, need error validation