added Refund Handling (firs code)

So I added Refund Handling for my Store.
Unfourtanely I could’t finish it but I did get to finish the frontend. So what did I do.
I updated the library page so its now easier to see that you can actually refund the game and how long you have until its not possible anymore.

For the backend I currently have some problems with the real refund. You cant really get the money back because of how the buying of a game currently works.
Especially automated refunding would be extremly hard in the current system.