Remove isConflict method from Interactions class

PHYS-16 #time 10m

This now resides in the MyShape class
Use new ShapeList method for conflict checking

PHYS-16 #time 5m
Delete RoundShape class.

PHYS-16 #time 15m

I made this class ages ago, when I thought that planning for everything
that could ever conceivably happen was the best approach when designing
classes. All it's done since this project's inception was complicate
things and increase compile times.
Delete MyEllipse class

PHYS-16 #time 10m

This class won't be used anytime in the foreseeable future, so I'm
axing it.
Delete StraightShape class

PHYS-16 #time 10m

This was just one more of the over-planned and unnecessary classes that
I made ages ago.