Ability to modify transactional email templates via the dashboard

[kieckhafer]

An expansion of #423 and #1429, this ticket concerns adding the ability to edit transactional emails from inside the dashboard, by admin users.

This ticket should include work that:

• Creates a new schema for email templates
• Takes the file-system HTML email templates and loads them into the correct Collection
• Creates a raw HTML editor (text-area) inside the dashboard that allows templates to be changed and saved into the collection. Fields should include:
  • Email Subject
  • Email Body
  • Email Language (en is default)
  • Title
• Checks to see if a template is inside the database, and if so uses that Template. If it's not inside the database, the file-system email will be the fallback.