Reminders with push notifications

[trobonox]

Add a due date to each card, send a push notification when the due date has been hit. Also show the due date on the card and mark the status using a color, for example no color for a due date which is still far away, orange for a due date which is close (1-2 days) and red if the date has been hit or is overdue (past the date).

• [x] Due date
• [ ] Push notification