Credit Ken for his wallpapers

Summary:
Since D26531 landed, it's now very obvious who made what wallpaper. Most wallpapers use
the actual artist's name, with one odd exception: the ones by Ken Vermette. This is both
unfair to Ken, and also inconsistent as we used Santiago's name for Ice Cold and Nuno is
listed as the creator of Elarun. Let's credit Ken properly. :)

Stable branch since these names aren't translated.

Test Plan:

Reviewers: VDG, Plasma, ndavis

Reviewed By: VDG, ndavis

Subscribers: plasma-devel

Tags: Plasma

Differential Revision: https://phabricator.kde.org/D26808