Split up vagrant provisioning script

[kaedroho]

The script should be in two parts

• base.sh - Turns a precise32 box into a wagtail-base box
• project.sh - This takes the wagtail-base box and adds project specific configuration into it

If the user has built their own "vagrant-wagtail-base" box, the first script can be omitted (speeding up vagrant provisioning)

[gasman]

Do we gain anything from being able to build directly from a vanilla Ubuntu box? My feeling is that it's a pretty inconvenient option all round - both for us maintaining the script, and the fact that it takes about as long to install everything as it does to just download wagtail-base - and I'd be perfectly happy to ditch that.

I think the idea originated in https://github.com/torchbox/vagrant-django-template because we didn't want to deal with hosting the base image, but still wanted our Django projects to be publishable with no closed dependencies. vagrant-wagtail-base has been publicly downloadable from day one, so that isn't an issue here.