Refactored rake task into a class

 - Added dumper class and moved all the logic into that class.
 - fixtures_path method is not present in Rails 3 and requires Active
   Record's 'config_load' task to be run. So removed using it in
   fixtures_path method.
@prathamesh-sonpatki I guess I mentioned this, but using this would mean we support only rubies with keyword arguments.