Remove Aura's Promise implementation in favor of native ES6 Promises.

For browsers that don't support promises natively, the included
ES6Promise library will polyfill its implementation.

===

Add directory for existing polyfill files and move Json and Function.bind
polyfills.

ccollab review #674584
@P4CL:9437041@
@rev tmoss, byao, goliver@
@bug W-2355623@
Merge branch 'ksecretan/master-pending-ES6-Promises' of git.soma.salesforce.com:ksecretan/aura into bob/master-pending/pr135-es6promise
Merging origin/bob/master-pending/pr135-es6promise into master