Added require('material-design-icons').STATIC_PATH

[appsforartists]

It would improve the developer ergonomics if we made hosting this package as easy as possible.

For instance, if you are working on an app locally/offline and want to use Material assets, with this change you'd be able to:

server.map(
  STATIC_PREFIX + '/material-design-icons',
  require('material-design-icons').STATIC_PATH,
);

and all the icons in this package would be available at http://localhost:8080/static/material-design-icons/ Of course, you'd want something more robust for production, but this would be an improvement for development.

Thoughts, @shyndman, @jestelle?