Add mipmapping to player head icons

[Fueredoriku]

Solves #577

[toberge]

Seems to fix the issue, but it comes with the caveat of not having a dotted look on lower resolutions (the player heads look like they're regularly filled)

[Fueredoriku]

It's a good enough trade off I think, especially after testing some different alternatives (2* 2, 3* 3 and 4*4 checkerboards) that also produced the Moiré effect at noticable distances. Larger checkerboard patterns than that just looks bad in terms of pixel art imo