add logged_in? / login / logout methods to auth

* logged_in? - checks whether user is logged in, but not whether they have a valid key
* login - generates and returns a randomized key, and logs the user into the sql database
* logout - logs the user out from the sql database

the user still needs to have the cookies added / removed, which would be done in CricketBase. login and logout methods still need to be added to CricketSQL.