upgrade to react-router v4

[rahulbot]

There are some major changes that will require significant work. Lets think about whether this is worth it, and if so - when?

The migration guide has details. Good intro tutorial here. And here is a bit on integrating with redux.

related to #546

[rahulbot]

Here's an intro to integration with cookies - https://medium.com/@rossbulat/using-cookies-in-react-redux-and-react-router-4-f5f6079905dc

[cindyloo]

currently still on: "react-router": "^3.0.5", "react-router-redux": "4.0.8",**