Fixes has_many conditions in Rails 4.1

Rails 4.1 passes the association into the scope lambda, not the class.
Rather, the associated object's class is available within the context
of the lambda as `model`.
Use DatabaseCleaner 1.2 for testing against Rails3 and lower to avoid compatibility erros between Ruby18 and DatabaseCleaner >= 1.3
close #372; Use Arel for SQL construction on VersionConcern for cleanliness; fix VersionConcern#index so it also sorts by primary key when possible
Typo fix on CHANGELOG [ci skip]
Update contributors on README [ci skip]
Add spec validating sort order of versions association by default
Merge pull request #373 from patbenatar/fix/rails-4.1-has-many-association

Fixes has_many conditions in Rails 4.1
Update CHANGELOG [ci skip]
Update specs checking for truthiness and falseyness to use syntax avoiding RSpec deprecation warnings [ci skip]
Add Rails Engine class; reorganize rails framework dir
Autoload models via the PaperTrail::Rails::Engine if the gem is being used within Rails