This commit finishes up the implementation of newChainControlFromConfig
in order to properly initiate the members of the chainControl struct
when the new light client mode (neutrino). With this lnd is now able to
switch over to either mode with a simple configuration change.
This commit adds a new agent to the codebase: the chainRegistry. In a
multi-chain future, the chainRegistry will be the dispatch point
capable of mapping cross-chain parameters, and a particular chain to
the chainControl for that chain. The chainControl struct encompasses
the 3 primary interfaces used within the daemon to register for events,
and drive other workflows.
