Add 3 new focus stealing policies

Globals:

* tyrannical.settings.block_children_focus_stealing = true --Block popups ()
* tyrannical.settings.group_children = true --Force popups/dialogs to have the same tags as the parent client

Tags:

* no_focus_stealing --Prevent new clients from selecting the tags (good for chat windows), make the new client "urgent" instead

Also update the documentation to match those additions