Implement the news button

Make the news button open the latest news post in the user's web
browser.

Also remove the webkit dependency. I was planning on using it to
display the news in a custom window, but we'll just use the user's
browser for now.

gui/MainWindow.h

@@ -87,6 +87,8 @@ slots:
 
 	void on_actionMoreNews_triggered();
 
+	void newsButtonClicked();
+
 	void on_mainToolBar_visibilityChanged(bool);
 
 	//	void on_instanceView_customContextMenuRequested(const QPoint &pos);