Higher quality server platforms icons

My minor suggestion(s):

- raise the quality of the icons of the server platforms
- make the Velocity icon more visible (bad contrast)
- the PaperMC logo changed: https://papermc.io/images/logo-marker.svg

<img width="482" alt="Screenshot 2021-07-13 123045" src="https://user-images.githubusercontent.com/60609373/125437474-46bfce5d-2578-4007-bab5-30ebcccb8e87.png">
