Move mildenhall theme from /var to /usr
The mildenhall themes are located in /var/lib/MILDENHALL_extensions. Move this directory to /usr/share when building OSTree images. Add a symbolic link so that unmodified binaries can still run.
Apertis: https://phabricator.apertis.org/T5362 Signed-off-by: Frédéric Dalleau frederic.dalleau@collabora.com