Multi-peer with consensus #205
Description
In PeerNetworkInterface, pass all ChainSync results to the Consensus module (see #201), which will then indicate which blocks to fetch based on its chain selection.
Note this is still manually configured with a topology file.
The main difference from 204 is that it now takes it's preferred chain from consensus.
The PeerNetworkInterface will need to decide which of N upstreams it has offering a particular block to ask for it - it can round robin but also take a view on quality of node & connection.