Add knowledge attribute to player.
Add list of completed classes to each player.

This list will be used to keep track of whether the player has
completed a particular class or not.
Adding a few classes to university.

Each class has a title, a knowledge_value that the class will add
to the player, a time cost for taking the class, a base
knowledge_required before taking the class, and a prerequisite
class_required if necessary.
Added symbols for the classes at the university.