Feature: AK Preference poll
This MR depends on !268 (merged), on !270 (merged) and on !276 (merged). Previous development was on felix_bonn/akplanning!22 (closed)
This MR adds the app AKPreferencePoll with forms to poll the AK preferences of participants.
The CSS for the polling view is working but could probably improved on.
Further, the fields poll_published_at and poll_hidden are added to Event to control the opt-in into preference polling.
Edited by Felix Blanke