Bulk Email Multiselect (#12301)

TNL-4356

Allows multiple bulk email targets to be specified at once.

-The previous "All" option has been split into "Staff" and "Learners"
-The backend changes made here lay the groundwork for cohort emailing
-The data migration, 0005, is somewhat large and requires deploy attention
-Tests have been updated
-Numerous safe-commit-linter fixes are included

lms/djangoapps/instructor/tests/utils.py

@@ -51,6 +51,20 @@ class FakeEmail(FakeInfo):
         'created',
     ]
 
+    class FakeTarget(object):
+        """ Corresponding fake target for a fake email """
+        target_type = "expected"
+
+        def get_target_type_display(self):
+            """ Mocks out a django method """
+            return self.target_type
+
+    class FakeTargetGroup(object):
+        """ Helps to mock out a django M2M relationship """
+        def all(self):
+            """ Mocks out a django method """
+            return [FakeEmail.FakeTarget()]
+
     def __init__(self, email_id):
         super(FakeEmail, self).__init__()
         self.id = unicode(email_id)  # pylint: disable=invalid-name
@@ -61,6 +75,7 @@ class FakeEmail(FakeInfo):
         hour = random.randint(0, 23)
         minute = random.randint(0, 59)
         self.created = datetime.datetime(year, month, day, hour, minute, tzinfo=utc)
+        self.targets = FakeEmail.FakeTargetGroup()
 
 
 class FakeEmailInfo(FakeInfo):
@@ -91,3 +106,4 @@ class FakeEmailInfo(FakeInfo):
         fake_email_dict = fake_email.to_dict()
         self.email = {feature: fake_email_dict[feature] for feature in self.EMAIL_FEATURES}
         self.requester = u'expected'
+        self.sent_to = [u'expected']