Added a magnitude function to Point.
Added implicit conversions from Point to Point2d and Vector2d
Added a new kind of hackeyclosestPointOfIntersectionWithArbitraryPath
and a few other additions to PathPlanning
Added closeEnough to Point2d.
Created PlanetTest.java to test getPositionIn()
Fixed several related bugs in abstractOrbital and Planet which were
causing problems with getPositionIn().

1. calculateDisplacement was actually updating the orbitalAngle causing
getPositinIn to change the state of the Planet

2. the planet's displacement from its parent was being applied twice
during getPositionIn