Create templates for accepted, waitlisted, rejected emails

[grahamhoyes]

• Can use templates from previous years as inspiration, see here: https://github.com/albogdan/makeuoft-site-2.0/tree/master/application/templates/mails. Create just .html templates.
• Accepted should have a link to the dashboard, and include how many days they have to RSVP.
• See the account activation email template for how to include links to the dashboard.
• Email content: https://docs.google.com/document/d/1d-7FqIHiEVl0ysVCZ3efASYGdVw4fEUfNvWbJCYnRSs/edit