An admin can view applicants/applications

* Modify admin::hall_assignment controller
* Modify admin::halls controller
* Modify routes file
* Admin::applications show
* Admin::applications new
```ruby
flash[:notice] = "#{@application.user.email}'s application has been approved"
```

PLEASE STOP MAKING THESE TWO STRINGS.

DON'T KNOW WHERE YOU LEARNED THIS.

PLEASE UNLEARN IT.