* instead of sending the the control messages (e.g. handshake reply,
sys msg ack) via the normal message send ingress point they are
now injected via side channel and will therefore not go through
higher level stages such as handshake and system message delivery
* UID exchange with handshake stages
* second iteration of reply side-channel, observable
* InboundContext and OutboundContext to facilitate testing
without real transport
* collapse ArterySubsystem and Transport into ArteryTransport
* incomplete HandshakeRestartReceiverSpec (origin address missing
to be able to implement that part
* remove embedded aeron media driver directory on shutdown