jquery-ui: update to latest stable (v1.11.1)

The current version (v1.10.4) is now called "legacy". The new stable version
has a different directory layout; it no longer splits css/ and js/ directories.
Since the *.js files refer to the *.css files by relative paths, I'm not
splitting them. Everything now goes to "$out/js/".

Also, upstream removed version numbers from filenames, so we don't need to
create those version-less symlinks anymore.