Added a common interface for Triangle and ConvexPolygon called Polygon. 
	-This actually shouldn't matter if we're going to use ConvexPolygon
over Triangle anyway, but it doesn't hurt to have it in there if we're
keeping the Triangle class in the submission.
	-Changed some of the methods to use the Polygon interface for
parameters instead of ConvexPolygon. These methods with ConvexPolygon
still exist as comments but will most likely be removed before
submission.

Also made a few adjustments to the friction.