Change grpc.proto field names to snake_case
Change grpc.proto field names to snake_case

Java client code can still use the camelCase field naming convention,
and other language bindings will not be forced to do the same.

Snake_case field names are also recommended in the Protocol Buffers
Sytle Guide:  https://developers.google.com/protocol-buffers/docs/style

bitsquare/bitsquare,bitsquare/bitsquare