GRPC communication.

[bartossh]

Starting from the wallet service I would like to propose adding GRPC (protobuf) communication for the few reasons:

• Single message schema to be used for any software to communicate with the wallet (Java, Python, NodeJS, C++, C, Rust, GO, name it)
• Type system in the message.
• Small message size.
• Faster than http1.1 and http2
• Encryption on the message level
• Streaming possible on message level.

Later we can expand this and move networking from HTTP to GRPC.