using class(es) instead of object(s) where appropriate

With reference to [Sandi Metz rules for developers](http://robots.thoughtbot.com/sandi-metz-rules-for-developers) and since [single responsibility principle](http://en.wikipedia.org/wiki/Single_responsibility_principle) sounds more appropriate when referred to a class as a whole, thus making appropriate changes. 

Please feel free to let me know your thoughts on this in case you think I'm missing something or I need to incorporate something else.

Thanks.