That means we can now have highlighters active at global, buffer, and
window scope. The add-highlighter and remove-highlighter syntax changed
to take the parent path (scope/group/...) as a mandatory argument,
superseeding the previous -group switch.
That means we wont have a very nice interaction between show_whitespaces
and column highlighters, but thats the simplest fix for now, if we want
a better behaviour we need to introduce a way to know that a replaced
range is splittable (meaning it means to have the same amount of columns
as the range it replaces)
Fixes#1275
