Move dataset path to redux / react-router

[trvrb]

Currently logic of dataset path (ie /flu/h3n2/3y vs /zika/) is handled through direct manipulation of window via changeRoute in App. This should be moved to redux / react-router. We'll have stored state in redux and use router.push to update URL.

I'd propose to put this in store.controls alongside colorBy, layout, etc..., where store.controls.dataset still follows the scheme set up by @rneher in parseParams.

[jameshadfield]

Keeping this open for now, but moving to backlog, as we aim for launch.

For launch, RR will handle some paths, but parseParams will still be employed for the virus dataset logic.

[trvrb]

We've just decided that the current setup with react-router loading App (https://github.com/nextstrain/auspice/blob/master/src/index.js#L41) and then App querying the URL (https://github.com/nextstrain/auspice/blob/master/src/components/app.js#L77) is the right way to go.