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.
this might break multi-packet updates. The server may have to send different properties of an entity in multiple packets in which case the client will get two packets with the same edit time... but we don't want to ignore that second packet. You can test this by setting a very large (~1300 byte) property for script, url, userData, or some other "string" property.