Add some Interactions methods to MyShape

PHYS-16 #time 20m

Add mergeWith, calcMergedAngMomentum, and calcMergedRadius to MyShape
class.
Use new MyShape.mergeWith method for Interactions

PHYS-16 #time 5m
Add comments to new MyShape methods

PHYS-16 #time 5m
Remove transferred methods from Interactions class

PHYS-16 #time 5m
Delete old methods from Interactions

PHYS-16 #time 10m
Move several Interactions methods to Simulations

PHYS-16 #time 10m

Moved the following functions:
  getSplitBodyRadius
  randomSplitBodyPlacement
  randomSplitBodyPlacementInZone
  randomSplitBodyMomentum

These had zero business being in the Interactions code. The only place
they were even being called was over in Simulations.
Comment new Simulations methods.

PHYS-16 #time 5m
Use typedef'ed Simulation pointer throughout class

PHYS-16 #time 10m

This makes any future modifications to the type of object returned by
the Simulations methods much simpler, in addition to being easier to
read.
Delete pointless conflict method.

PHYS-16 #time 5m