[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.

fontcolor = 'black'
bgcolor = '#FFFFFF'
stylesheets = sheet['stylesheets'] + ['%s/mycube.css' % datadir_url]