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
Scratch my comment, this was just really confusing. It makes it look like anything requested for the frontend would go through this. Should add a comment on how the property isFrontEnd is set since this is really not clear