change it so all topics MUST include a category, we store a special uncategorized category to compensate

this cleans up a bunch of internals and removes some settings

spec/controllers/categories_controller_spec.rb

@@ -58,7 +58,7 @@ describe CategoriesController do
                               }
 
           response.status.should == 200
-          category = Category.first
+          category = Category.where(name: "hello").first
           category.category_groups.map{|g| [g.group_id, g.permission_type]}.sort.should == [
             [Group[:everyone].id, readonly],[Group[:staff].id,create_post]
           ]