An admin can view applicants/applications

* Modify admin::hall_assignment controller
* Modify admin::halls controller
* Modify routes file
* Admin::applications show
* Admin::applications new
If you swap the if and the else it would make this cleaner:

```erb
<% if @application.approve %>
  <%= button_to "Unapprove", admin_application_path(@application, approve: false), method: :put %>
<% else %>
  <%= button_to "Approve", admin_application_path(@application, approve: true), method: :put %>
<% end %>
```