Add short instruction for building images.
Add xfce4-screenshooter.
Remove live-config-sysvinit.
Merge branch 'master' of github.com:digabi/digabi-os

* 'master' of github.com:digabi/digabi-os:
  Add xfce4-screenshooter.
Reject http/https before client target allows it
Remove bogus reject rule
Fix PolicyKit hook filename.