Publish a pre-configured vagrant VM

Currently we specify a [generic Ubuntu 12.04 Vagrant basebox](https://github.com/mrdavidlaing/pressupbox-development-boilerplate/blob/master/Vagrantfile#L115-L116) and then do all the customisations onto that base box via [a provisioning script in the Vagrantfile](https://github.com/mrdavidlaing/pressupbox-development-boilerplate/blob/master/Vagrantfile#L124).

Rather than starting from a generic base box, we should start from a base box that has already had the provisioning script run against it once before.  

Running from a poor internet connection you at least know upfront exactly how much software will be downloaded (its all encapsulated in the initial base box ~ 800MB); so you can plan to do that overnight.  

Then, when you're actually sitting at the keyboard typing `vagrant up` for the first time you should have a more speedy first boot experience.