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

app/schemas.py

@@ -365,7 +365,7 @@ class TemplateSchema(BaseTemplateSchema, UUIDsAsStringsMixin):
 
     @validates_schema
     def validate_type(self, data):
-        if data.get('template_type') in [models.EMAIL_TYPE, models.LETTER_TYPE]:
+        if data.get('template_type') in {models.EMAIL_TYPE, models.LETTER_TYPE}:
             subject = data.get('subject')
             if not subject or subject.strip() == '':
                 raise ValidationError('Invalid template subject', 'subject')
@@ -391,6 +391,7 @@ class TemplateSchemaNoDetail(TemplateSchema):
             'template_redacted',
             'updated_at',
             'version',
+            'broadcast_data',
         )