Fix tests

main_app_spec was not updated to reflect removed MainApp routes.
Fix .main-video display issue

The main page did not stretch the height of .main-video to fill-in empty
space. This was due to the recent addition of a <div> in the app's index
view (views/index.erb) whose height was not 100%.
Add admin functionality to front-end

This requires several back-end changes to support. API /current_match
PUT route has improved data validation and sanitation functionality to
account for the number of things that may go wrong with the front-end.
Most of these adjustments prevent serious app crashes.

API /login POST return value now includes permissions. The app
determines which 'main' page to go to. Users with 'admin' permission
cannot be anyways, so they are taken to a new admin page.

authenticate() helper now returns a user instance. This allows easy
retrieval of user permissions.