Rails4 support

The following changes enable Rails 4 support for this gem.  Highlights for these changes include:

* Remove ```attr_accessible :name``` from Role model.
* Role controller behavior now includes using of ActionController::Parameters permit method, only if StrongParameters is defined.  Otherwise controller params are normal Rails 3 params.
* ```attr_accessible``` is added to Role model dynamically through an initializer file if the application to which this engine is mounted utilizes Rails 3.
* All tests now pass.
* Test build now contains the ability to pass a Rails version through an environment variable so that the gem can be tested against multiple versions of Rails.  Documentation outlined in README.