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 we generally name the fixture, ex: for a user table, record `john` or `nancy`. How about trying to get name for an object by doing `to_param`, or something similar? This can be done later, just a thought.