Fix hook situation for Skin::doEditSectionLink
The old hook supplied a way to override the HTML used for the section link,
but two extensions both trying to use it was obviously not going to work.
Deprecate it in favour of a hook that goes around gathering info to build
the initial HTML, then shoves it through the old hook for back-compat.
So that WikiEditor can add in extra URL parameters as well as VE adding in it's