Webapp changes for move of interactives to the top-level dir.

The interactives saved in static files where moved to public. This caused a
number of problems, (URL conflicts,  save and import errors, …).
The top level URL for interactives served from the web app is now /webapp.
Rails test changes for moving of interactives to top-level dir
remove hostname from md2d url
Fix model urls in webapp interactives
Saving the model's modelOptions attributes
Prevent scripting errors when creating interactive copies