Automatically duplicate site index.html for each page route during deployment

[JedWatson]

Ref #36

We've got copies of the index.html page for each possible route at the moment in the site/src folder.

It would be nice to automatically create the copies as part of the gulp publish task (will probably require changes to the react-component-gulp-tasks package to support this)

[NogsMPLS]

Would using something like this help? https://github.com/shinnn/gulp-gh-pages

If bringing in another dependency either here or in react-component-gulp-tasks is okay, I'll look into it a bit further.