web_renderjs_ui: use context-free getDocumentValueList for reference lookups

When looking up a document by reference, using getDocumentValueList from
the context of a web site / web section might not find the documents,
depending on the predicates defined on the web site / web section.
2 jobs for master in 0 seconds
Status Job ID Name Coverage
  External
passed SlapOS.Eggs.UnitTest-Master.Python2

00:17:09

passed SlapOS.Eggs.UnitTest-Master.Python3

00:14:05