2.0.0-alpha001

Removed generic ServiceManager (HeaderDefinition provides header implementation from this point on).
Replace HttpWebRequest based client request with HttpClient based implementation.
Add IXRoadRequest, IXRoadRequestHandler<TRequest, TResponse> type for improved typing support.
Remove XRoadSerializable base class requirement. Use XRoadSerializableAttribute to mark serializable types.
Use ITrackSpecifiedMembers interface when member deserialization info is needed.
Operation definitions extracted from request type attributes and IXRoadRequest definition.