(Feat/login page) Finish login page

In reference to issue #17 
I decided not to include the "Create An Account" button since the OAuth buttons should either login or initiate a signup. 

Flow:
* OAuth login with FB or Twitter
* After authentication, app does a DB query to see if user exists and determine if they're a restaurant or a customer. 
  * If user doesn't exist: we redirect to the signup page which should ask if they're a restaurant or customer. Depending on which one they click, we serve them the appropriate signup form to enter any additional information Twitter/Facebook doesn't pass back to us. 


For existing users, after clicking OAuth, there should probably be a db lookup to see if they already