Replace app icon
I found an icon that @mbruchert made a long time ago for pix that seems to no longer be in use (https://phabricator.kde.org/D27220):
I modified it slightly since we don't really have the "pixelated" aspect of the name that pix has.
@mbruchert do you give consent do use this icon here under CC-BY-4.0?
Edited by Devin Lin