This moves the lightwalletd client code to a separate Gradle module, but does not yet do much clean up the public API (e.g. hiding generated GRPC objects). That will be a followon change via #673
I’ve prototyped a safer version of the API that would be implemented for #673 for two specific calls: obtaining the current block height and obtaining the light wallet info. These were the easiest endpoints to update and they provide a useful exploration for the future changes needed.