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

db/migrate/20130515193551_add_auto_close_days_to_categories.rb

@@ -0,0 +1,5 @@
+class AddAutoCloseDaysToCategories < ActiveRecord::Migration
+  def change
+    add_column :categories, :auto_close_days, :float
+  end
+end