Redirect users to contact form when allow_registration_edits is false and prefill it

[FinnIckler]

Gets rid of another of those pesky banners and allows users to contact the organizers with a prefilled template.

@danieljames-dj I know you worked on the contact form, is this the way I should interact with it to prefill it? I noticed you had the message property already there, but you wasn't using it