Since entries in the database tying entities to accounts only can be
created if the entity already is created in the database we need to make
sure the relation in "accounts_entities" isn't created until the entry in
"entities". This is done by letting the StorageManager handle it.
The way to interface between the Persistance and the StorageManager
classes isn't obvious, so we'll have to do it by signals.
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.
