- don't try to include version in static_urls that don't point to files
- use full static_urls (with extension) for backbone and underscore, so version can be computed
closes#5141
this model does not work with the comm/widget communication model.
We need to be able to load the dependencies before we send the
show() message to the widget manager. Otherwise a race condition
will exist where the widget manager may recieve the show message
before the dependencies have been loaded (happened almost every time).