Vagrant base

A nearly complete 'custom base image' change to the vagrant workflow - this allows for much quicker new dev environment startup times, especially if you use a locally cached copy of the image - helpful over conference wifi.

**NOTE**: This PR is incomplete, someone still needs to upload `gittip_box.box` to a public location, and change `http://FIXME` in both the Vagrantfile and README.md to point to the new URL.