Make player a nested resource of user

Add player as singular resource to the user resource. A user should only
have one player profile.
Add user object to the player controller for look up. Since a player
model is now tied to a user. We look up a user first then find that
user's player profile. The user look-up is either by checkinc Devise's
current_user method or from params in the routing.
The player's _form also has a known bug with routing to a singular
resource so I had to specify the URL where the form goes to.
Update test cases for the changes.
Clean up tests

Forgot one test file for the sessions and clear out the test for player
model for now. Will need to redesign it.