In order to be able to register the subservers with the root grpc server
before we have all dependencies available, we wrap them in an
GrpcHandler struct. This struct will initially hold an empty reference
to the subservers, which allows us to register with the GRPC server, and
later populate and create the subserver instance.
We now use the jsonpb marshaler to convert the RPC responses to
JSON in lncli and REST. The jsonpb has a setting to use the
original name as defined in the proto file and the explicit
json_name definition is not necessary any more.
The jsonpb setting is called OrigName and needs to be true.
