4K resolution support

[dkurzaj]

Hello, I just launched CupCarbon on my 4K screen and, as you can see on the following picture, the interface is absolutely not scaling and it is very painful to use. It would probably be interesting to fix since more and more laptops will probably have that type of screen in the future. I faced this issue on a common Dell XPS laptop running Linux Mint with the Cinnamon desktop environment.