Support user maintenance of email templates

[dleehr]

• Templates should be editable/maintainable by users
• Template sets are tied to groups, and users can only be in one group. This doesn't fit the real-world use cases very well.
• Django admin can facilitate this editing, but needs finer-grained permissions

[dleehr]

Summary of template notes from meeting 2017-04-26

• README is geared towards developer end.
• Description on how that works
• Templates. Do you have access to use different templates that are context-specific
  • specify which template through client.
  • message file in client
  • customization and different templates/data types or contexts.
  • consider a template of naming conventions
  • if I send from personal account.
  • Handoff data from own account.
  • local templates

[dleehr]

Related to #106

[dleehr]

This issue was created before datadelivery-ui, but such a template editing system is more of a UI feature

Some thoughts:

• prompt users to preview/edit templates before they create deliveries
• Provide simple template editor, displaying possible template variables in-line (currently documented on DukeDSClient Wiki)
• Include basic preview mode for email templates in UI app - just a modal would be fine.

[dleehr]

Our current plan is now to require users to contact us before they can send deliveries, and is being implemented. So user management of templates is not part of the milestone.