Create a page for updating Communities.presentation_a, b, and c, which can be null or a datetime.
Create some linkage between the 'edit alignment' page and 'edit presentation dates' page. Maybe a checkbox that reads "Add a presentation date for this community" that redirects the user to the presentations page upon successful form processing. (unnecessary, since 'edit alignment' isn't a thing anymore)
Confirm that town_meeting_date field is no longer needed and then remove it.
Communities.presentation_a,b, andc, which can be null or a datetime.town_meeting_datefield is no longer needed and then remove it.