SCOPING: Expanded email functionality - reminder emails, feedback, expanded records

Nobody has claimed this yet.

Plan out additional tools for email to participants and create separate issues per feature.

These tools will allow researchers to use the email functionality more easily, and to more flexibly communicate with families. Preliminary list:

1. Automatically email new feedback to participants if they've opted in. (Make a new email preference about this.)

2. A researcher would ideally be able to specify messages to send on a particular schedule for longitudinal participants, e.g. sending up to N total automatic messages per study of the following types:
* To anyone who last participated at least N days ago and has not received this message since that session. (Stop after X emails or Y sessions.)
* To anyone who has completed at least N sessions (e.g., send a thank-you after the user completes two sessions)

3. A user would ideally be able to opt out of emails from a particular RESEARCHER as well as by type of email. This is so that if e.g. they've decided not to continue a particular study and don't want to hear about it anymore, they could opt out of those emails without opting out of all reminder emails. Or so that if one research group sends much more email they don't affect the opt-out rate as much for everyone else.

No file, test, or entry point is named. Start by reviewing the existing email functionality in the Python API, then split the three preliminary capabilities into separate issues with clear scope and completion criteria. Done means each proposed feature has its own actionable issue.

Written by the indexing model from the issue text.