New: Investigate Email Notifications

[micahp2]

We need to find out what it would take to create, receive, and send emails related to the creation, editing, upcoming notice and end of a Circle session.

The needs are for the Keepers to have Totem handle the tasks of:

• alerting users when they are added to a session
• letting users know X days out from a session starting
• reminding users within Y hours of a session starting
• notifying users of any changes to a session's info, date/time, state, etc.
• informing users of a cancellation of a session
• alerting users when they are removed from a session (they leave, they are kicked out, etc.)
• Gathering responses from users, asking if they are attending or not

@blopker has suggested looking into this email service provider to see if they offer capabilities to build on for these tasks: https://developers.mailerlite.com/docs/#mailerlite-api