Allow organizers to send one-time notifications with feedback survey

[Igor Santos]

The organizer would initially need to create a survey in one of the suggested systems (google docs, survey monkey, typeform) and provide a link. We would send a predefined email with that link. The link should be verified if it's from one of those providers - if not, it would need to be moderated by administrators before being sent.

This would ensure organizers would not use this feature to spam users with messages regarding other subjects.