Flatten out protobuf wrappers

[jaganseshadri]

The protobuf wrapper class mimic the structure of the message defined inside the .proto files.
Pros:

• Provides namespace organization synonymous with the protobuf definition.
  Cons:
• Loses out on namespace abstraction that makes it easier for people who don't know either gRPC or protobuf or both to work with it, i.e. it's still laborious to know which message needs what attributes to be set.

Proposed solution:

1. More documentation would definitely help.
2. Flatten out the protobuf definition, i.e. bring out some nested attributes to the parent level.