Improve newsletter list subscribe function

...s/0318_districthomepage_ecomail_newsletter_list_source.py

...tions/0156_mainhomepage_ecomail_newsletter_list_source.py

majak/settings/base.py

...0008_makeawishroot_ecomail_newsletter_list_id_and_more.py

...ions/0009_makeawishroot_ecomail_newsletter_list_source.py

make_a_wish/migrations/0010_makeawishroot_fbevents_id.py

make_a_wish/models.py

shared/models/main.py

shared/utils.py

...ons/0131_uniwebhomepage_ecomail_newsletter_list_source.py

uniweb/migrations/0132_uniwebformpage_show_in_parent_page.py

...rations/0133_alter_uniwebflexiblepage_content_and_more.py

uniweb/migrations/0134_uniwebhomepage_fbevents_id.py

uniweb/templates/uniweb/blocks/embedded_subpage_form.html