JumpTime, Iterations/frame, units

Finalized units--including time which is now displayed in days.
Changed jumpTime method to be more accurate with orbitals
Changed fast forward to iterations/frame
Encapsulated gravity calculations into one method
It's not immediately clear which functions are using what unit of time, jumpTime uses days where as GravityMotionIteration uses hours? I would either make sure all functions are using the same unit of time or make it apparent what functions use what. You could either:
* Add a comment above the function the says what unit of time it's using
* Make this clear using the parameter/function name:
    void jumpTimeInDays(float days)