Move scheme client to grpc wrapper style

Breaking changes:

• change return type of SchemeClient::list_directory from grpc type to own described type for prevent problem in feature - if need to change protobuf lib or code generator settings

Other:

• Add connection manager - one place for get connections
• Add grpc wrappers - small code for convert calls and types from grpc internal types. Internal types have very similar structure to grpc, but more comform usage in code.
• Move discovery and scheme client to grpc wrappers and connection manager.