[#666] Including a Vagrant setup

This Vagrant setup uses Ansible as provisioner, and a Ubuntu 14.04 base box. Using NFS for shared folders, as it provides better performance.

It was tested with a Ubuntu 14.04 Host machine. If someone could test it on OSX, that would be great!

Instructions were included in the CONTRIBUTING and Readme files. For now, you'll need to login to run `rails s` after provisioning the server. We thought this would be better for development, since it provides more rich debug information.

This Vagrantfile have been working just fine with all the people that uses Phansible.com, so I guess yes :) This is just to check if we should use the default method or the hacking with shell script to run the provisioning on Windows hosts.

But I'm not a Ruby person, so I don't know if there's something wrong with it.