Enhancement: Upgrade React Router to its Latest Version

[rwieruch]

React Router has a lot of breaking changes when using the latest version. Maybe it would be a great PR to upgrade react-router (perhaps also react-redux-router or even get rid of it) to its latest version.

[chriszhangusc]

Working on it.

[chriszhangusc]

I have finished the router upgrade, however, I want to propose some changes:

1. Change browse URL from http://localhost:8080/browse?genre=Minimal to http://localhost:8080/browse/Minimal because in react router v4 we need to parse the query string, the second way it will make the code easier and cleaner to parse the genre from URL.
   See:

2. Simplify the App Logo to point to browse the default genre, right now it is pointing to the currently selected route.

3. Probably a typo: change filename from constants/authentification to constants/authentication.

[rwieruch]

Everything sounds great! I would say, go for it 👍

[rwieruch]

#40 perfectly done by @minipekka