replace default background for HeaderBar by a wallpaper from Breeze

Summary: replace default background for HeaderBar by a wallpaper from Breeze

Test Plan: wallpaper from Breeze with an LGPLv3 license compatible with elisa license

Reviewers: Elisa, VDG, astippich

Reviewed By: Elisa, astippich

Subscribers: astippich, januz, andreaska

Tags: Elisa

Differential Revision: https://phabricator.kde.org/D9847