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.
Removing the hasGravity() and isRestingOnSurface() checks here allows an external physics engine to set the velocity of an entity to zero (perhaps caused by some resting collision that this simulation is not aware of) and thus disable simulation of the entity on this end.  Otherwise this simulation would constantly bounce the entity and "fight" with the other simulation through the EntityServer.

Basically, this change is required in order to demo bullet working on one end and a simple extrapolation simulation working on the other.  In theory: eventually this simple extrapolation algorithm will only be run only as a last resort: when there is nothing it can fight with.  At that time it may make sense to add back the check for gravity in this special case.