Minor Update: React Router to V4

Some fixes and updates.

• Added AuthRouter custom helper for your authenticated routes. There are a lot of solutions out there, but i prefer this one, easier.
• Removed Index component wrapper. It's no use after the update, but if you want this some kind of parent component that does something globally, go on and make one!

If you are more comfortable on using the React Router version 3 please use the previous version of this!
Goodluck and happy coding!