View source for Writeable directories preserved during updates of Atomic Desktop

Base directories stored as a diff against the image, changes preserved using 3-way merge with diffs stored per-deployment
* /etc
Regular writeable directories
* /var
Directories symlinked to /var to make them writeable
* /home -> /var/home
* /mnt -> /var/mnt
* /opt -> /var/opt
* /root -> /var/roothome
* /srv -> /var/srv
* /usr/local -> /var/usrlocal
Directories overlayed to /var to make them writeable
* /usr/share/sddm/themes -> /var/sddm_themes/themes