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

spec/factories/events.rb

@@ -17,7 +17,6 @@ FactoryGirl.define do
 
     factory :event_full do
       difficulty_level
-      track
       after(:build) do |event|
         event.commercials << build(:event_commercial, commercialable: event)
         event.difficulty_level = build(:difficulty_level, program: event.program)

spec/factories/tracks.rb

@@ -3,5 +3,6 @@ FactoryGirl.define do
     name { Faker::Commerce.department(2, true) }
     description { Faker::Lorem.sentence }
     color { Faker::Color.hex_color }
+    program
   end
 end