[#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.

@erikaheidi This command should help with bundle install issues:

    shell: bundler install chdir=/vagrant --path vendor/bundle -j1