Conditionally require jquery.uls.data as dependency, if ULS is available

Due to changes in ULS, it will no longer "just be there".

It needs to be specified as a dependency, although for Wikibase,
not a hard dependency.

Change-Id: I02a1b61277483ed160c700a5bf13363af093a880
(cherry picked from commit 24d8660a3345b8f194550f99f72eff1613999b8d)