create property on the base object for rpc method and path

[pyramation]

@liujun93 can add color and also has some ideas about adding more types and info as well

cc @Zetazzz

[pyramation]

I think we already have the "path" prefix, it's actually the protobufPackage property which we already export https://github.com/confio/cosmjs-types/blob/7bc6fa0547abc2471f76f77cffb406bd8929d06a/src/cosmos/tx/v1beta1/service.ts#L9

so we may likely only need to add the service name