Switch from `when` to `bluebird` for Promise implementation.

Bluebird is very fast.

Change-Id: I713f1d9c4313c4da8ffa0a381496a787ad405d64
Switch from `bluebird` to `es6-shim`/`prfun` for Promise implementation.

Use standard ES6 promises.

Change-Id: I61718099b756cc089cbf9c112080721c06c29661