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/categories.js

@@ -386,3 +386,5 @@ Categories.filterIgnoringUids = function (cid, uids, callback) {
 		},
 	], callback);
 };
+
+Categories.async = require('./promisify')(Categories);