Resolve value of OBJECT_PATH type to a real proxy object

[vbuell]

Similarly to ORMs where one-to-one/one-to-many relations can be automatically dereferenced by the getter, dasbus could do same for values of OBJECT_PATH type. Something like

property_x = bus.get_proxy('org.MyService', '.../Controller').GetPathById('some_id').PropertyX

or

property_x = bus.get_proxy('org.MyService', '.../Controller').GetPathById('some_id').to_proxy().PropertyX

instead of:

path = bus.get_proxy('org.MyService', '.../Controller').GetPathById('some_id')
property_x = bus.get_proxy('org.MyService', path).PropertyX

That would significantly simplify the client's code as dereferencing work can easily be 25% of all dbus related code.