Adds a new lnrpc API that lets the caller get ("dry run") the scores that would be given to a set of node by the available autopilot heuristics.
As go modules allow us to build outside of the GOPATH, we shouldn't look for .proto imports there anymore.
This commit adds a new service lnrpc/autopilot, that is to be used to communicate with the running autopilot. Currently a RPC for getting the status of the agent is included, as well as enabling/disabling at runtime.