Setup basic Revision History page

Sets up paper_trail tracking in important models

and add conference_id to versions for storing conference_id
of conference related objects  as metadata.This will help in querying
for versions related to conferences.

Fix issues with factories & event types initialization.Import paper_trail testing helpers
Fix bug: Creating an event creates a useless version with event update

Add revert and view changes features to revision history

app/models/events_registration.rb

@@ -4,9 +4,17 @@ class EventsRegistration < ActiveRecord::Base
 
   has_one :user, through: :registration
 
+  has_paper_trail meta: { conference_id: :conference_id }
+
   delegate :name, to: :registration
   delegate :email, to: :registration
 
   validates :event, :registration, presence: true
   validates :event, uniqueness: { scope: :registration }
+
+  private
+
+  def conference_id
+    registration.conference_id
+  end
 end