add Vagrantfile for VM setup using VirtualBox

prerequisites:
- install VirtualBox
- [install vagrant] (http://docs.vagrantup.com/v2/installation)

To setup and start the VM, on the command line in the paparazzi directory:
`vagrant up`

This will fetch a 32bit Ubuntu precise image, provision it (install the paparazzi packages and xfce) and then start the VM.

You can now run `vagrant ssh` to log in to the development environment.
The `~/paparazzi` directory in the VM is actually the `paparazzi` directory in your host operating system -- changes in either directory show up in the other.

```
$ vagrant ssh
# cd paparazzi
# make
# ./paparazzi
```

Beware that this will sync the complete paparazzi directory on your host system with the ~/paparazzi dir on the VM!
Not sure if that is what most people would want...?