Reminder policies

Use the Live Sessions area in Django administration:

• Reminder timing policies define choices such as one day, one hour or five minutes before.
• Reminder channel policies enable a channel, expose it to instructors and choose whether it starts selected.
• Manual reminder policy enables “Send reminder now,” sets its minimum interval and allowed channels.
• Public live-session notification policy controls opt-in channels for public sessions.
• Reminder message templates map an event and channel to an approved provider template.

A channel selected by default must also be enabled and instructor-selectable. Retire a timing policy instead of changing its offset after instructors have used it; create a new timing when the meaning changes.