Add editable templates for bulk email

Adds the edX Marketing-approved template as html default.

lms/djangoapps/bulk_email/admin.py

@@ -3,7 +3,8 @@ Django admin page for bulk email models
 """
 from django.contrib import admin
 
-from bulk_email.models import CourseEmail, Optout
+from bulk_email.models import CourseEmail, Optout, CourseEmailTemplate
+from bulk_email.forms import CourseEmailTemplateForm
 
 
 class CourseEmailAdmin(admin.ModelAdmin):
@@ -16,5 +17,45 @@ class OptoutAdmin(admin.ModelAdmin):
     list_display = ('user', 'course_id')
 
 
+class CourseEmailTemplateAdmin(admin.ModelAdmin):
+    form = CourseEmailTemplateForm
+    fieldsets = (
+        (None, {
+            # make the HTML template display above the plain template:
+            'fields': ('html_template', 'plain_template'),
+            'description': '''
+Enter template to be used by course staff when sending emails to enrolled students.
+
+The HTML template is for HTML email, and may contain HTML markup.  The plain template is
+for plaintext email.  Both templates should contain the string '{{message_body}}' (with
+two curly braces on each side), to indicate where the email text is to be inserted.
+
+Other tags that may be used (surrounded by one curly brace on each side):
+{platform_name}        : the name of the platform
+{course_title}         : the name of the course
+{course_url}           : the course's full URL
+{email}                : the user's email address
+{account_settings_url} : URL at which users can change email preferences
+{course_image_url}     : URL for the course's course image.
+    Will return a broken link if course doesn't have a course image set.
+
+Note that there is currently NO validation on tags, so be careful. Typos or use of
+unsupported tags will cause email sending to fail.
+'''
+        }),
+    )
+    # Turn off the action bar (we have no bulk actions)
+    actions = None
+
+    def has_add_permission(self, request):
+        """Disables the ability to add new templates, as we want to maintain a Singleton."""
+        return False
+
+    def has_delete_permission(self, request, obj=None):
+        """Disables the ability to remove existing templates, as we want to maintain a Singleton."""
+        return False
+
+
 admin.site.register(CourseEmail, CourseEmailAdmin)
 admin.site.register(Optout, OptoutAdmin)
+admin.site.register(CourseEmailTemplate, CourseEmailTemplateAdmin)