Improve Vagrant configuration

- I added support for the XVFB, which means I can run cucumber tests in a headless mode.
- I removed the postgres configuration from the vagrant file, which means that `rake db:create` works 100%, no need to create the database on the Vagrant::Provision.

- I added a *set_locale* cookbook, which means goodbye to the LATIN1 error when creating UTF-8 databases manually inside the VM.

- Also added the ruby-2.0.0 to the rubies list on rvm, so contributors can prepare the codebase to work on the latest release.


Tha's it. Thanks!