This change takes us away from using overflow:hidden on body by
default, only toggling this using a new `open` class when the navbar
has been expanded. `open` is toggled on body in the same places as it
is for the appear and navdrawer.
The open-source team at Google have requested that all HTML, CSS and JS
files include the relevant copyright headers before we can flip the
switch on moving this to github.com/google.
Adding them in as requested.
Also add a blank basic.html page. The idea with the index is to demonstrate
some simple usage - this is just a small starting point, but it would be good
to add some navigation for the styleguide and include some more getting started
pointers.
