more correct creation and edit times for entities

Fixing some bugs that I introduced when I split out EntityItem::_lastSimulated time from EntityItem::_lastUpdated and EntityItem::_lastEdited.

The bugs were not noticeable under normal conditions, but became noticeable when trying to get results from one physics simulation (bullet) to be relayed across the EntityServer and into another interface instance that was running a simpler simulation.  The update packets from the EntityServer were getting rejected at the receiving end because the accompanying _lastEdited time was too old.
Running two interfaces and the stack on a single host could cause the difference between _lastEdited and remote/adjusted values to be zero.  Since the EntityServer echos all changes back to the submitting interface, we must discard zero length differences to prevent an echo feedback loop.