Add a Vagrantfile to help lazy people to test Kanboard.

How to use :

* Install Vagrant (http://www.vagrantup.com or apt-get install vagrant)
* Install VirtualBox (https://www.virtualbox.org/ or apt-get install virtualbox)
* Inside the root directory, run : vagrant up
* Go to http://localhost:8080/index.php
* Login with admin / admin