Create up-to-date basebox to reduce initialisation time

This could simply be a newer version of janihurs' box, with apt-get update & upgrade already run. I still want to keep the current model of explicit dependency installation in the Vagrantfile (otherwise we get a "black box" and that defeats much of the purpose of having a recipe).

It would also enable switch of VM, however XFCE is quite a good compromise already.
