Ml/react native (aws-amplify#200)

* add cognito js lib and update references

* update cognito lib

* update node version and package deps

* update cognito sdk and auth test

* update with yarn workspaces and modules

* add lint to test

* update test cmd

* update build cmds

* update concurrency with bootstrap

* update deps, yarn should use local

* add build before test for workspaces

* remove package-lock.json

* update rn package

* update deps on react native

* update user attributes

* update docs

* core change

* Update package.json

* Adds a podspec for CocoaPods support

* update docs with cli instructions

* update quick start

* update crypto lib for react native and polyfill methods

* move core logic to aws-amplify

* updates for platform detection

* fixes for auth persistence

* update user agent in RestClient to use Platform

* update readme for PR aws-amplify#201

* only set user-agent on API calls in RN

* Remove unused JS call for verifiedContact