One-click "Remind Me" button on study page

**TL;DR**: A one-click button for people interested in participating in a study to receive a reminder at the date and email of their choice.

**Narrative**
"As an Experimenter on a study recruiting newborns, I would like to have a way for parents expecting a newborn child to very easily "sign-up" ahead of time, before their child is born, to receive a reminder about the study at a specific date in the near future (e.g. on the child's due date). the user would look at the study summary, click a "Remind Me" button, select a date of their choice on a pop-up calendar ("Remind me on..."), and enter their email or phone number ("Send a reminder at...") -- without leaving the study page. ". Clicking on the button triggers a reminder about the specific study at the date specified by the user. Ideally the user could opt to further "snooze" the reminder. The user shouldn't need to have a child registered on Lookit to do this.

No files, tests, or implementation entry points are named. Start by tracing the study-page and API entry points involved in study summaries, then define the reminder flow and its storage and delivery requirements. Done means an unauthenticated visitor can request a study reminder for a chosen date and contact method, with optional snoozing if supported.

Written by the indexing model from the issue text.