Migrated the RoboVM backend to use the new CocoaTouch bindings

The new CocoaTouch bindings will be introduced in the next release of RoboVM which will be out later this week. The old bindings will still be included as well for a couple of releases. This PR updates the backend and the iOS versions of all demos to use the new bindings.

BTW, did I sign the libgdx CLA? Can't remember. :-)