Add Vagrant support

I've added a Vagrantfile (complemented by a Puppet manifest which pretty much only installs Python and dependencies) so if anyone wants to set up Syte they can do it in a disposable virtual machine. What's missing is a helpful post-`vagrant up` message to let the user know what's next, i.e. that they need to set up `personal_syte_settings.py`.

Something else that I was thinking about is Docker support: if I get around to it, lightweight LXC containers can be used in place of full-blown VMs; and deployment to a Docker-enabled host would perhaps be as simple as building and shipping the appropriate image.

P.S. I also took the liberty of removing psycopg2 from requirements.txt since Syte doesn't seem to use a database...?