Ww3 feature/security fix

Increases the security by just putting in a user in the URL as ?user=username  and includes a session timout. 

To test:

1.  Change the session timeout to a ridiculous low number (it's in seconds), like 10.  Try changing the dates on an assignment and you should get an error in the js console and then a login window.  
2. In the URL bar: put webwork3/courses/maa101/manager?user=profa  and change the username to users enrolled, but without proper permissions, as well as users that aren't in the course.  I decided to just redirect them to /webwork2, but maybe something more informative is better?