Allow use of a mediawiki message to '''override''' the group used to group a special...

Allow use of a mediawiki message to '''override''' the group used to group a special page.
Form is specialpages-specialpagegroup-$specialpage
Tim suggested letting a message override the group to let someone with a better hand at organization in the community try organizing the pages. So we could then import those changes back into MediaWiki at some point in time.