Remove banner style comments from pb.proto
Remove banner style comments from pb.proto

The bisq-grpc-api-doc generator needs comments spefic to protobuf
message definitions, not groups of message defs.  This kind of
information can be included in the message specific comments.

Also changed some existing comments, and added others to suggest
a commenting style for .proto message and field defs.

bitsquare/bitsquare,bitsquare/bitsquare