Added Vagrant for unified development env.

Created a vagrant file, a provisioning script, and some supporting documentation. 

As mentioned in the provisioning script, this isn't really my forte, but I figure the perfect is the enemy of the good. I've gotten `npm start`/`grunt run:dev` up and running, though, so I'm hoping I can pass the baton off to folks with more experience in the actual HabitRPG code.