WIP: add meta package for Unity 8

Two options right now:

• Get the lightdm integration working, so Unity 8 can be launched as user
• Launch Unity 8 as root (less good :) )

main/postmarketos-ui-unity8/60-lightdm-autologin.conf

+# This file gets removed with postmarketos-ui-unity8, even if modified!
+[Seat:*]
+autologin-user=username
+autologin-user-timeout=0
+autologin-session=unity8