Create db table for email_templates

@DSASanFrancisco/portal-members

Creates the table to store an email template to send to a list of users.

This assumes that we want to have a 1:1 association with email templates and committees. That means we'll need to associate an email alias or a list of email addresses, to a committee. An alternative would be to associate an email alias directly on the email_templates table, and we would either get rid of the committee association or keep it but not for sending emails.