rules: Add support for :all qualifier Some layout options require to be applied to every group to maintain consistency (e.g. a group switcher). Currently this must be done manually for all layout indexes. This is error prone and prevents the increase of the maximum group count. This commit introduces the `:all` qualifier for KcCGST values. When a rule with this qualifier is matched, it will expands the qualified value (and its optional merge mode) for every layout, e.g. `+group(toggle):all` (respectively `|group(toggle)`) would expand to `+group(toggle):1+group(toggle):2` (respectively `|group(toggle):1|group(toggle):2`) if there are 2 layouts, etc. If there is no merge mode, it defaults to *override* `+`, e.g. `x:all` expands to `x:1+x:2+x:3` for 3 layouts. Note that only the qualified *value* is expanded, e.g. `x+y:all` expands to `x+y:1+y:2` for 2 layouts. `:all` can be used in combination with special layout indexes. Since this can lead to an unexpected behaviour, a warning will be raised.