[MOD] Add Category feature, to the wiki setup. 
Categorize structure pages requires categories. By moving categories to the same level, the structure detail page can make the display of the categorize.. option dependent on the category feature.
Remove Category from the Main features page.

git-svn-id: file:///var/local/code.tiki.org/tikisvn/trunk@47625 b456876b-0849-0410-b77d-98878d47e9d5