Added gems for testing purposes.

I found an article written by Aaron Sumner, where he explains how to do
good testing with rspec-rails, factory_girl, capybara and other gems. I
liked it, tested it and it feels good enough for me to integrate in the
day-to-day work I am doing.

For reference:

http://everydayrails.com/2012/03/12/testing-series-intro.html
http://everydayrails.com/2012/03/12/testing-series-rspec-setup.html
http://everydayrails.com/2012/03/19/testing-series-rspec-models-factory-girl.html
http://everydayrails.com/2012/04/07/testing-series-rspec-controllers.html
http://everydayrails.com/2012/04/24/testing-series-rspec-requests.html