[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.
bgcolor = '#000000'
stylesheets = ['%s/cubicweb.css' % datadir_url]
logo = '%s/logo.png' % datadir_url
lazy = lazystr('%(bgcolor)s')