*+Description+*
Copy Pasting portals doesn't work. The Portal case is missing in 
GraphModelImp.CanPasteNode method.
*+Initial setup+*
GraphTool Experimental, Unity 6.2

*+Reproduction steps+*
# Instantiate 2 nodes
# Connect them
# Replace the connection by portals
# Try to copy/paste a portal

*+Expected behaviour+*
The portal is copied with its connection.

*+Actual behavior+*
Nothing is copied

*+Logs and Links+*
(Add links to Yamato jobs, links to logs, and add a stack trace in this section)