Moved main template to index.php

Main.php was acting as the landing page for the website. It makes more
sense to make it the wordpress landing site rather than create a
separate page for it.
Renamed default roles to professor and student

These names better reflect the role of the user when browsing and
interacting with the website.
Reduced size of top banner
Disables the admin bar for non-administrators

Functionality for the admin bar has not been implemented for users.