Allow customization of the preview template on a per-preview basis.
Allow customization of the preview template on a per-preview basis.

Reviewers: jeff, dcramer, matt

Reviewed By: jeff

Differential Revision: http://phabricator.local.disqus.net/D4662

disqus/django-mailviews,joshowen/django-mailviews,disqus/django-mailviews,xavierdutreilh/django-mailviews,paxnovem/django-mailviews,joshowen/django-mailviews,danxshap/django-mailviews,xavierdutreilh/django-mailviews,paxnovem/django-mailviews,danxshap/django-mailviews