Hedgewars, King Arthur's Gold, Paraview and Gmsh icon added.

Hi! This is my first commit. I've created icons for _Hedgewars_, _King Arthur's Gold_, _Paraview_ and _Gmsh_ following the guidelines in [numix-wiki](https://github.com/numixproject/numix-wiki/wiki/Guidelines). If there is something to change tell me, I'll fix it as soon as possible.

Hedgewars: http://www.hedgewars.org/
King Arthur's Gold: https://kag2d.com/en/
Paraview: http://www.paraview.org/
Gmsh: http://geuz.org/gmsh/