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_get_template.py

@@ -3,7 +3,7 @@ import pytest
 from flask import json
 
 from app import DATETIME_FORMAT
-from app.models import TEMPLATE_TYPES, EMAIL_TYPE, SMS_TYPE, LETTER_TYPE
+from app.models import (TEMPLATE_TYPES, EMAIL_TYPE, SMS_TYPE, LETTER_TYPE,)
 from tests import create_authorization_header
 from tests.app.db import create_template, create_letter_contact
 
@@ -44,6 +44,7 @@ def test_get_template_by_id_returns_200(
         'name': expected_name,
         'personalisation': {},
         'postage': postage,
+        'broadcast_data': None,
     }
 
     assert json_response == expected_response