Now that the dispatch is handled in the property class, it can
be non-virtual, and completely removes the need for a lookup to get the
property instance.
All IG code should use the interface of LocatedEntity when dealing
with any entity, rather than sometimes requiring Entity. Add virtual
functions to the interface where required, and modify all other interfaces
to stop them using Entity. This makes the code way cleaner, and much better
de-coupled.
