Initial TouchBar Magic

* Make the AtomNSWindow also a NSTouchbarDelegate
* Implement basic makeTouchBar and makeItemForIdentifier methods
* Initial sending of touch / update events through IPC to BrowserWindowObjects

TODO:
* JS API
* JS Object Converters
* Generalize methods so that popovers can work

atom/browser/native_window_mac.h

@@ -100,6 +100,7 @@ class NativeWindowMac : public NativeWindow,
   void SetAutoHideCursor(bool auto_hide) override;
 
   void SetVibrancy(const std::string& type) override;
+  void InitTouchBar() override;
 
   // content::RenderWidgetHost::InputEventObserver:
   void OnInputEvent(const blink::WebInputEvent& event) override;