Separate the session manager in a monitor and policy part.
The monitor manages the devices and endpoints.
The policy watches the nodes/ports/clients and applies the policy
of linking them.
Because both now have a separate connection, we can remove some
hacks in the protocol. When a remote was both the implementer and
user of an object we could get in a deadlock when the user was
blocked waiting and the implementator was blocked sending a reply.
We used to un-busy a client when it was expecting a reply from a
ping or sync for this reason.
Add and use some more keys for the endpoints and streams.
Remove override for resources, it can't work in general.
Rename method to add_object_listener to add a listener for
events/methods from the remote object.
Rename some methods to _call to call the interface and _notify
to notify the listeners.
Remove unused client event to be notified of resource
implementations.
