Add Promise polyfill to version control. Promise objects
are included in ECMAScript 6 and browser support is
present, but non-universal. Using the polyfill approach
permits the use of Promise directly throughout the
application without relying on bleeding-edge browser
support.
Promises are useful at the framework level particularly
because of the number of asynchronous calls made when
assembling bundles. Framework layer is WTD-518.
