Add support for both positional and named arguments in RPCs

API written by hand like RemoteOmShard and RemoteGovernance is forcing client to use positional arguments invocation style.This become problem once smae API is implemented in other language (or generated from YANG) using named arguments invocation style.

This improvement is about

• provide API methods in existing interfaces to support both invocation styles
• add special case handling in proxy code that will delegate invocation of default method to interface itself, rather then do real proxying