Resolve "Redis connector unregister do not unregister"
Description
Fixed symmetry issue in connect_slot/disconnect_slot: when calling connect_slot the given callback is wrapped into
a QtThreadSafeCallback object, when calling disconnect_slot with the same callback the comparison to find out if
topics really need to be unregistered (from _topics_cb and from Redis, eventually) has to be done on the same
QtThreadSafeCallback object.
Closes #165 (closed)