Localize flash messages

I've moved the flash message strings into YAML locale files so that they can be localized and customized by the application.
I've also added tests for the controllers to verify that the expected messages are set and that I18n.t is called, as well as a Travis-CI config to test against Rails 3.2 and 4.0 with Ruby 1.9.3, 2.0, and 2.1