Web application manifest sample.

@addyosmani @ebidel @PaulKinlan @cwilso (and anyone else who might be interested):

Here's a basic example of a page that uses a `manifest.json` to specify web app capabilities/metadata.

The `manifest.json` is pretty bare right now, so if there's something specific you think it should demonstrate, your feedback is welcome.

You can try it out at https://rawgit.com/jeffposnick/samples/web-application-manifest/web-application-manifest/index.html using Chrome 39+ on Android.
We're following the pattern of linking to the chromestatus.com page from each sample, which in turn has links to the spec, as well as implementation status in other browsers, links to other demos, etc.