An admin can mark and unmark users as RMs or RAs

* Implement namespace routing to have admin functions
* Admin controller to ensure a user is an admin
* Admin directory (controller/views) to house the admin functions
* Add custom validation in User model
Make a new `<li>` for each message in the `full_messages` collection. 

```
<% @user.errors.full_messages.each do |message| %>
...
<% end %>
```