sysutils/desktop-installer: Update to 0.8.0

Replace SLiM login manager (unmaintained for 10 years) with SDDM
SDDM also automatically detects multiple desktop environments (DEs)
Add SDDM option for Gnome, LXDE, LXQT
Other minor enhancements to streamline package install sequence

Changes: https://github.com/outpaddling/desktop-installer/releases