create, edit and use email branding instead of organisation

notable things that have been kept until migration is complete:

* passing in `organisation` to update_service will update email branding
* both `/email-branding` and `/organisation` hit the same code
* service endpoints still return organisation as well as email branding

tests/app/dao/test_email_branding_dao.py

@@ -0,0 +1,44 @@
+from app.dao.email_branding_dao import (
+    dao_get_email_branding_options,
+    dao_get_email_branding_by_id,
+    dao_update_email_branding,
+)
+from app.models import EmailBranding
+
+from tests.app.db import create_email_branding
+
+
+def test_get_email_branding_options_gets_all_email_branding(notify_db, notify_db_session):
+    email_branding_1 = create_email_branding(name='test_email_branding_1')
+    email_branding_2 = create_email_branding(name='test_email_branding_2')
+
+    email_branding = dao_get_email_branding_options()
+
+    assert len(email_branding) == 2
+    assert email_branding_1 == email_branding[0]
+    assert email_branding_2 == email_branding[1]
+
+
+def test_get_email_branding_by_id_gets_correct_email_branding(notify_db, notify_db_session):
+    email_branding = create_email_branding()
+
+    email_branding_from_db = dao_get_email_branding_by_id(email_branding.id)
+
+    assert email_branding_from_db == email_branding
+
+
+def test_update_email_branding(notify_db, notify_db_session):
+    updated_name = 'new name'
+    create_email_branding()
+
+    email_branding = EmailBranding.query.all()
+
+    assert len(email_branding) == 1
+    assert email_branding[0].name != updated_name
+
+    dao_update_email_branding(email_branding[0], name=updated_name)
+
+    email_branding = EmailBranding.query.all()
+
+    assert len(email_branding) == 1
+    assert email_branding[0].name == updated_name