Draft: Apply display settings to GDM session

This MR builds over !1580

This commit changes the way this works. Instead of launching the daemon as the GDM user, it is launched as root. It copies the monitors.xml file into /etc/xdg, and generates a dconf db file that is stored at /etc/dconf/db/gdm.d, and compiled.

Unfortunately, although the monitors.xml do work, the dconf part doesn't.

Merge request reports