fix(bs) remove concrete refs to swarm and dht
refactor(bs, core) rename bitswap objects
feat(net:service) add sender interface
todo(blockservice, core) add notes

* to wrap datastore for ease of use
* to pass a non-responsive bitswap mock rather than performing nil
* checks internally
feat(bitswap) add interface
refactor(blockservice) use bitswap.Exchange interface
allow service to have nil handler

@perfmode this means we can create a Service first, give it to
the network and protocol (removing interdep).
bugfix: service has a Start func

We were issuing handling goroutines in both NewService and Start
Service: remove RequestID from SendMessage
Move Sender interface to network pkg

@perfmode sender is exactly what we need to pass in to dht/bitswap.
better protobuf Makefile with wildcard.
expose handler in inet
core dht setup
goroutine note comment
simpler, clearer dht message
starting on dht-- msg handler
handleGetValue
refactor symbol
lint nit
ping + find peer