message: remove class that has been moved into data_model.h
diff: @@ -61,43 +61,6 @@ private:
  };
  -template<typename T>
  -class model_subscription
  -{
  -public:
  - model_subscription(std::shared_ptr<XXX::wamp_session>& ws,
  - std::string uri,
  - T handler)
  - : m_uri( std::move(uri) ),
  - m_event_handler( std::move(handler) )
  - {
  -
  - auto fn = [=](wamp_subscription_event e)
  - {
  - if (e.type == wamp_subscription_event::update)
  - m_event_handler.on_event(e.details, e.args.args_list, e.args.args_dict);
  - };
  -
  - ws->subscribe(m_uri, {{KEY_PATCH, 1}}, std::move(fn), nullptr);
  - }
  -
  -
  - template<typename... MArgs>
  - model_subscription(std::shared_ptr<XXX::wamp_session>& ws,
  - std::string uri,
  - MArgs&... args)
  - : model_subscription( ws, uri, T( args... ) ) // delegate construction
  - {
  - }
  -
  - const std::string& topic_uri() const { return m_uri; }
  -
  -private:
  - std::string m_uri;
  - T m_event_handler;
  -};
  -
  -
  class basic_list
  {
  public:
  