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
if the call fails (hr != S_OK), string value may not be correct. Should we update the function here to return HRESULT (ie. only use string when HRESULT is S_OK)? Or we can stay with void but we reset the string to be Empty or NULL in the case of failure? Thoughts?