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.
It would be great if you could specify the expected densities of the icons. The algorithm being used to pick the right icon use in priorities icons of the right density.

The optimal size is 48x48 for density=1, then you have to multiply by the dpi.