An issue arose that shh_newMessageFilter was routed to the upstream instead of local node. This PR fixes that. It also revisits routing logic and makes all requests go to the local node by default.
This PR refactors RPC subsystem for status-go:
cleans up two different RPC client implementations (RPCManager and rpc.Client)
creates new package under geth/rpc
moves routing logic into this package (rpc.(*router))
add tests for routing
cleans up NodeManager