Add and inherit from ApplicationRecord to match Rails 5.0 style

plugins/documents/app/models/document.rb

@@ -1,4 +1,4 @@
-class Document < ActiveRecord::Base
+class Document < ApplicationRecord
   include ActsAsTree
 
   belongs_to :created_by, class_name: 'User', foreign_key: 'created_by_user_id'

plugins/messages/app/models/message.rb

@@ -1,6 +1,6 @@
 require "base32"
 
-class Message < ActiveRecord::Base
+class Message < ApplicationRecord
   belongs_to :sender, :class_name => "User", :foreign_key => "sender_id"
   belongs_to :group, :class_name => "Group", :foreign_key => "group_id"
   belongs_to :reply_to_message, :class_name => "Message", :foreign_key => "reply_to"

plugins/wiki/app/models/page.rb

@@ -1,4 +1,4 @@
-class Page < ActiveRecord::Base
+class Page < ApplicationRecord
   include ActsAsTree
 
   belongs_to :user, :foreign_key => 'updated_by'