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

app/dao/email_branding_dao.py

@@ -0,0 +1,23 @@
+from app import db
+from app.dao.dao_utils import transactional
+from app.models import EmailBranding
+
+
+def dao_get_email_branding_options():
+    return EmailBranding.query.all()
+
+
+def dao_get_email_branding_by_id(email_branding_id):
+    return EmailBranding.query.filter_by(id=email_branding_id).one()
+
+
+@transactional
+def dao_create_email_branding(email_branding):
+    db.session.add(email_branding)
+
+
+@transactional
+def dao_update_email_branding(email_branding, **kwargs):
+    for key, value in kwargs.items():
+        setattr(email_branding, key, value)
+    db.session.add(email_branding)