Dilator.stop() now shuts everything down, and returns a Deferred when it all
stops moving. This needed some Manager state machine changes (to notify
Dilator when it enters the STOPPED state). This also revealed problems in the
delivery of connector_connection_made() (which was misnamed) and
connector_connection_lost() (which wasn't being called at all).
This is only used by tests so far (and will simplify the integration test
that hasn't landed yet), but is not yet wired up to Boss, so there's no way
for applications to enable it yet.
I mistakenly believed that Noise handshakes are simultaneous. In fact, the
Responder waits until it sees the Initiator's handshake before sending its
own. I had to update the Connection state machines to work this way (the
Record machine now has set_role_leader and set_role_follower), and update the
tests to match.
For debugging I added a `_role` property to Record, but it should probably be
removed.
only install 'noiseprotocol' (which is necessary for dilation to work) if the
"dilate" feature is requested (e.g. `pip install magic-wormhole[dilate]`)
