Integrated react-router

For #1 . Feel free to ask any questions. Decided against `react-router-bootstrap` in the end because it was never really finished, won't ever be and we can do without. `react-router` has a flexible and well-documented API:  https://github.com/rackt/react-router/tree/master/docs/api
But you made me realize the little `res.locals` detour *really was superfulous*! There should just be one "front-end routes" controller that just takes care of returning that `index.html` file, what do you think?