Support attachments for message templates, scheduled reminders

The UI for Message templates and Scheduled reminders does show attachments. We've found that if they are added in the schema then they will show up if the template is selected to send a message to an individual. Despite the deliverability issues associated with attachments, we have some clients that want to use attachments. I think adding this support would be quite simple, sort of a cut and paste / refactor and reuse for these screens.