Adds the creation of a Web App Manifest when creating an App

[marchant]

https://w3c.github.io/manifest/
https://developer.mozilla.org/en-US/docs/Web/Manifest#Browser_compatibility
https://developers.google.com/web/fundamentals/engage-and-retain/web-app-manifest/
https://developers.google.com/web/updates/2014/11/Support-for-installable-web-apps-with-webapp-manifest-in-chrome-38-for-Android