[cwproperties] refactor properties form to make it partly overrideable easily (closes #1936782) also fix some pitfalls on the way: * shouldn't capitalize labels, this has to be done in translation files as desired * form_row in CWProperties form didn't return subform as its parent class

# copyright %(year)s %(author)s, all rights reserved.
# contact %(author-web-site)s -- mailto:%(author-email)s
#
%(long-license)s
"""%(distname)s specific hooks and operations"""