add new routing strategy

Following on from this tutorial[1], we are trying
to the best way to organise our Express routes. We think
this technique works the best. ref #4

[1]: http://start.jcolemorrison.com/quick-tip-organizing-routes-in-large-express-4-x-apps/
refactor /api/user route into it's own seperate dir, ref #4
add main route in index.js + fix base route in api-user.js, ref #4