[Grace-core] Grace and GTK plus

[Kim Bruce]

I have added NotesOnGraceGTKPlus in the ObjectDraw2013 directory in the repository.  They explain the GTK features used in defining the objectdraw library.  You will notice that these are used, for example, in the objectdraw library in defining the class aGraphicApplication so that we can add GUI components to different parts of the window.  The file ClickerWButton.grace shows how to add a button to a window (though it doesn't work quite correctly in the javascript implementation because we don't have a mechanism to read from files at runtime).
 
Kim