Bump various gems

Bump rails, multi_json, and several test related gems. Also remove,
refactor and/or bump a few other gems in the Gemfile. Needed to
tweak the spec_helper a bit after this to support the changes.
Refactor translations integration tests

Moved to features dir as per new version of Capybara. Also changed
matchers as the within syntax was failing for odd reasons. Lastly
modified the test that uses Selenium to use a local Firefox instance
instead of going out to Perry's old
http://translatable-qa.herokuapp.com/ app sitting on Heroku.
Deleting old file