API Token

* In each controller we used to call before_filter authenticate_user!. Created my own method that handles this.
  * Checks for auth_token parameter and logs a user in if it is valid.
  * If auth_token parameter is absent or token is incorrect, redirects user to sign_in page and calls the authenticate_user! method from before.
* Added tests for authentication token stuff, I can expand on it later but I'm tired.

For: #42