Add option to setup local dev environment with Vagrant

This pull request adds the ability to automatically setup a working development environment with Vagrant.  It also makes a few minor changes to get the environment up and working:

1. Remove an unused attribute from the LegFile model that does not show up in the database dump
2. Sets default database credentials in the local settings template.  Also adds sponsor_links key.
3. References a specific commit for pdfminer

Instructions on how to get the dev environment up and running with Vagrant are in the Readme.md