add photo to form page

shared/templates/styleguide2/form_page.html

...s/styleguide2/includes/organisms/header/photo_header.html

.../styleguide2/includes/organisms/header/simple_header.html

uniweb/migrations/0119_uniwebformpage_main_image_and_more.py

...rent_header_uniwebflexiblepage_show_transparent_header.py

uniweb/models.py

uniweb/templates/uniweb/uniweb_flexible_page.html