Bower.json & reduced Modernizr file

I replaced the full Modernizr build with one just using the [CSS 3D Transforms](http://modernizr.com/download/#-csstransforms3d-shiv-cssclasses-teststyles-testprop-testallprops-prefixes-domprefixes-load) Pushy uses and made note of that in the README.md.

I also defined a bower.json package so that this can be registered with Bower. If you accept this PR, either of us can register it. See [bower.io](http://bower.io)