[uilib] Fix incorrect serialization of python dicts into javascript objects Valid javascript object keys must be surrounded by quotes unless they are valid javascript identifiers. Valid identifiers are a defined by complex and changing specs, so it is much simpler to always use quotes. Closes #17046704.

cubicweb source: source-is-missing cubicweb/web/data/jquery.flot.js line length is * characters (>512)