Revert "conform to new jquery-ui filenames"

This reverts commit 28702a2465bc3238a523838286af12e9308b43a1.
revert jquery-ui-rails gem to version 4

With version 5.0.0, delete links created by
link_to did result in a GET request.
With version 4.2.1 they correctly created
a DELETE request.
Merge pull request #1026 from ontohub/fix_delete_links

Fix delete links