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/conference.rb

@@ -9,7 +9,7 @@ class Conference < ActiveRecord::Base
 
   default_scope { order('start_date DESC') }
 
-  has_paper_trail
+  has_paper_trail ignore: [:updated_at, :guid, :revision, :events_per_week], meta: { conference_id: :id }
 
   has_and_belongs_to_many :questions