Allow user folder permissions to be updated

Updated the endpoint for `.set_permissions` to update a user's folder
permissions as well as permissions for a service. User folder
permissions are optional for now, since Admin is not currently passing
this data through.

app/dao/service_user_dao.py

@@ -0,0 +1,13 @@
+
+from app import db
+from app.dao.dao_utils import transactional
+from app.models import ServiceUser
+
+
+def dao_get_service_user(user_id, service_id):
+    return ServiceUser.query.filter_by(user_id=user_id, service_id=service_id).one()
+
+
+@transactional
+def dao_update_service_user(service_user):
+    db.session.add(service_user)