Add support for 'exec_once' property, add basic support for tag 'add' and 'selected' smart hooks
Fix multiple bugs and add support for tags on multiple screen

One of my 3 GPU died on me, so my screen layout chnaged. This allowed
me to find and fix a few bugs dealing with static conf on dynamic settup
Add support for non-exclusive tags
Fix bugs with intrusive clients when there is no tags selected
Fix focus_new