cleaned up logout code

removed logout option for displayusers page
logging out now closes displayclassesactivity instead of launching new
loginactivity
added authstatelistener to handle logout

re-added logout button to displayusersactivity
Cleaned up code for creating user

removed requirement for new user to input a course number, each activity
can now query for the userID without need to pass through intents.
Added click listener for user list
fixed bad cast in displayusersactivity