Add tabs to category create/edit modal. Categories can have a default auto-close setting that applies to all new topics created in the category. Add rspec-given and write some integration tests. Tests for topic auto-close with category default

app/serializers/category_serializer.rb

@@ -1,6 +1,6 @@
 class CategorySerializer < BasicCategorySerializer
 
-  attributes :secure, :groups, :available_groups
+  attributes :secure, :groups, :available_groups, :auto_close_days
 
   def groups
     @groups ||= object.groups.order("name").all.map(&:name)