escape elastica queries & bump pulq to legacy-bofp

Removes that backslash in front of every slug query string that nobody
knows why it's there in the first place (probably umlaut problems with
former versions of routes and slugs). The backslash at he beginning of
slugs was always added and leads to json/javascript unicode hex-code
interpretation errors on solr side. The queries are now escaped using
elastica's own static escapeTerm method.

refs #21321