Summary: Volna won the wallpaper competition, so time to add it to Breeze as the new default!

Test Plan: Apply patch, compile, and restart plasmashell

Reviewers: #vdg, #plasma, davidedmundson

Reviewed By: #plasma, davidedmundson

Subscribers: raveomelette, IlyaBizyaev, Luwx, ndavis, broulik, rikmills, plasma-devel

Tags: #plasma

Differential Revision: https://phabricator.kde.org/D26953