Cannot load pulses if PulseStorage is default registry

[lumip]

Using a PulseStorage object as default pulse registry prevents pulses from being loaded with a "Pulse with name already exists" error. Upon creation of the deserialized PulseTemplate object, it will try to register with the default registry (the PulseStorage object), which already has a pulse registered with that name (the serialization of the just deserialized pulse).

[lumip]

Demonstrated by new test in branch issues/301_pusle_storage_as_default_issue .