Refactor web request

There are 2 parts:
1. Upgrade Newtonsoft.Json to version 4.5.0.0
2. Refactor classes to restore consistency.
The Refactoring change:
  CouchResponse -> CouchResponseObject
  CouchWebResponse -> CouchResponse


This way CouchResponse is the counter-part of CouchRequest.
CouchResponseObject is thin wrapper around JObject contain the response.