Enhancements to the GraphView

Minor bug fixes and improvements!

Minor bug fixes and improvements!

Minor bug fixes and improvements!

- Add support for Composites

- Mark the document as edited when it is changed - Sort the positions before saving so the diff is trackable - Added 'Open with CoreDataGraph' when you right click on an `xcdatamodeld` file

- Minor bug fixes and improvements!

Minor bug fixes and improvements!

Minor bug fixes and improvements!

- The app now uses document based architecture

Minor bug fixes and improvements!

Minor bug fixes and improvements!