Brings the placeholder index.html more in line with WSK's basic.html

@addyosmani & @PaulKinlan, this updates the placeholder `index.html` to match what's found in https://github.com/google/web-starter-kit/blob/master/app/basic.html

If this looks to be what you had in mind, I'll update the individual samples to adopt the changes. 

Closes #4 
I'm explicitly including this `<link>` to `favicon.ico` since it's not in the browser default `/favicon.ico` location.

I'm not sure if there's a specific order that I need to put this in in relation to the other various icon definitions, or whether it's strictly needed, but I'm assuming if there are some browsers that don't recognize the `sizes="192x192"` icon then this would be used.

Happy to hear if I'm wrong and this isn't needed.