Since not all entities have physical location, which is more and more true
now that we have domains. Entities that are placed in non-physical domains don't have
any location data.
This also makes it easier to streamline the sending of properties, since we only need
to send the properties that actually have changed.
In addition, this helps with removing circular references, since the "m_parent" field no longer
is a Ref.
By appending the "!" character it's possible to modify a value. The possible modifications
are "append", "prepend", "subtract", "add-fraction" and "default". If nothing is specified "default"
is used.
An example would be "foo!append".
