Create an endpoint link object when linking endpoints. Keep track
of the links in the endpoint_link and cleanup when they are all
gone.
Improve properties on session objects.
Create a helper in the session manager to link all ports between
2 nodes.
Make the output endpoint call the input endpoint create_link, passing
the node or ports to link to.
Make the input endpoint complete the link by calling the session
helper to link all ports.
Remove the node policy, we're only using a policy for the endpoints
now.
Move all the media-session object monitoring into one place and
provide an API to get to the session objects.
Make API to add module specific info to objects.
Add methods to export and create objects in the session. This should
make it possible to link proxy to implementation and avoid a server
roundtrip in some cases.
