add broadcast to template_types and add broadcast_data

had to go through the code and change a few places where we filter on
template types. i specifically didn't worry about jobs or notifications.

Also, add braodcast_data - a json column that might contain arbitrary
broadcast data that we'll figure out as we go. We don't know what it'll
look like, but it should be returned by the API

tests/app/v2/template/test_post_template.py

@@ -97,7 +97,7 @@ def test_valid_post_template_returns_200(
 
     assert resp_json['id'] == str(template.id)
 
-    if tmp_type != SMS_TYPE:
+    if tmp_type in {EMAIL_TYPE, LETTER_TYPE}:
         assert expected_subject in resp_json['subject']
 
     if tmp_type == EMAIL_TYPE: