flag EntityItem when changed by update

When an entity gets an update we might or might not need to reflect its changes in the physics engine.  Some changes can have expensive consequences in the physics engine so we'd like to only update them when absolutely necessary.  To this end I'm introducing EntityItem::_updateFlags which will be used as an accumulator for changes that need to be handled.  I've added some EntityItem::updateFoo() methods that are used for data extracted out of packets and that will set the correct bits as properties change.