Refactor topics controller. Add Common abilities. Add destroy action.

app/models/abilities/common.rb

@@ -71,6 +71,9 @@ module Abilities
 
       can :create, Annotation
       can [:update, :destroy], Annotation, user_id: user.id
+
+      can [:create], Topic
+      can [:update, :destroy], Topic, author_id: user.id
     end
   end
 end

app/models/topic.rb

@@ -1,6 +1,4 @@
 class Topic < ActiveRecord::Base
-  include Flaggable
-
   acts_as_paranoid column: :hidden_at
   include ActsAsParanoidAliases