Allow Vagrant versions 1.0 with Virtualbox and 1.2 with VMWare Fusion or Virtualbox

This is the first draft of a Vagrant setup which works for both v1 and v2 configs. It does this by:
- Extracting out the common functions into `vagrant/Vagrantfile.common`
- Extracting out the provisioning into `vagrant/Vagrantfile.provision`
- Extracting out the Virtualbox config into `vagrant/Vagrantfile.virtualbox`
- Switches config function based on the Vagrant version and configures appropriately in `Vagrantfile`

It was working on Vagrant 1.2 with VMWare before I started refactoring, but I can't test that until I get back to my other machine. It definitely works on Vagrant 1.0 with Virtualbox as I am using that right now.