First version that sort of works
Make animation on error work
Add more animations
Remove trailing whitespace
Fix broken images
Refactor and clean up data model

* References are now stored in a consistent way.
* The internal schema is now fully normalized (e.g. the
  title/label isn't duplicated to referencing objects).
Move css to a separate file
Update select2 style to look like bootstrap input fields
Correctly update scissors when diagram connection is redrawn
Remove superfluous console.log statements