Promisify modules (#6723)

* WIP promisify

* promisify psql

* ability to skip some keys

* dont promisify client object

* remove async

* clone entire module so it has all properties

* add shim for node 6

* ignore sessionStore as well

* ignore pool on psql

src/notifications.js

@@ -608,3 +608,5 @@ Notifications.merge = function (notifications, callback) {
 		callback(err, data.notifications);
 	});
 };
+
+Notifications.async = require('./promisify')(Notifications);