Refactoring Student Team Controller

Hey Andrew. Please take a look at our recent changes to the Student Team Controller.

We've allready renamed it "StudentTeamsController" but we were also concerned that there is no such thing as a "StudentTeam", there is really only an "AssignmentTeam", so the controller should probably be "AssignmentTeamsController". That being said, the worker itself uses the current login more as the primary target. confusion here seems to be from the model structure used.

In addition, many of the more complicated management in the controller is record keeping-which we think would be better taken care of through relationships. Some of these relationships are allready in place in some way or another,  but some (like the `has_many :users, :through => :teams_user` in Team) are done in a non-standard way. Without extensive testing on both the controller and the models, we are a little nervose to make such sweeping changes. We also readily admit that none of us are testing experts or experts on the Expertiza system, so the "white box" testing we'll be doing will be pretty high risk. Do you have any advice?
This should be handled in the `action_allowed?` method, since it is authorization.