Revert "An Engine can include app/helpers, so let's move the helpers there"

This reverts commit 2ed8adfe37.

reason: Because mounted engines on the app doesn't search the main_app's helpers, then throws "undefined method `paginate'" in the views

app/helpers/kaminari_helper.rb

@@ -1,5 +0,0 @@
-require 'kaminari/helpers/action_view_extension'
-
-module KaminariHelper
-  include Kaminari::ActionViewExtension
-end

lib/kaminari.rb

@@ -26,6 +26,7 @@ EOC
 
 # load Kaminari components
 require 'kaminari/config'
+require 'kaminari/helpers/action_view_extension'
 require 'kaminari/helpers/paginator'
 require 'kaminari/models/page_scope_methods'
 require 'kaminari/models/configuration_methods'

lib/kaminari/hooks.rb

@@ -28,6 +28,10 @@ module Kaminari
         ::Plucky::Query.send :include, Kaminari::PluckyCriteriaMethods
       end
       require 'kaminari/models/array_extension'
+
+      ActiveSupport.on_load(:action_view) do
+        ::ActionView::Base.send :include, Kaminari::ActionViewExtension
+      end
     end
   end
 end