This is somewhat cleaner as the proxy's pipe and network setup
was awkwardly interleaved. It also means network's constructor
is free to use both; currently some code is working around the
fact that the response queue doesn't exist in the constructor.
We store it in the config object instead of in the blockchain object.
The blockchain object now refers to its config, and calls refresh_height() to update it.
The network objects also refer to the config rather than the blockchain.
This is the first of many small steps to untangle the verifier from stored state and so
permit the history tab to work in offline mode. The refactoring will simultaneously clean
up a lot of accumulated cruft.