Adapt to new structure introduced in jQuery UI 1.11.0

I gave it a try. It builds the assets and they seem to be correctly generated. But I didn't actually test the generated gem yet, while I intend to do it tomorrow. Anyway, there are lots of incompatible changes proposed in this PR to consider.
There is a stray `puts` here... Could you review the diff line-by-line please and make sure it's exactly the code you intended?

I believe the test app (in the `testapp` directory) needs updating as well for the new file names.

Let me know when you've re-pushed and I'll take a look again so we can merge this. Thanks again for putting this PR together! :)