Qualify all usages of classes from gnpy.core.elements
Qualify all usages of classes from gnpy.core.elements

This will be needed by one of the follow-up commits which move JSON
manipulation into a single file. We have to distinguish between "Roadm"
the JSON representation and "Roadm" the network element which propagates
spectrum.

Change-Id: I6888842c57c3a57849fabe75d0ff6f5bbfab426a

Telecominfraproject/gnpy