Fix for RPC application and allow overriding JSON serializer

• Feature - allow override JSON Encoder and Decoder by overriding *Serializer class
• Fix RPC application not liking when params attribute is not provided

Fixes for RPC client and application `request_id` value handling

Fix for "same-millisecond-generated request_id are identical" issue
Fix for "some error responses do not echo back request_id value" issue