Set up the database as part of the provisioning process.

I find it kinda fiddly to copy `database.sample.yml` and edit things
according to my local install. If we are going to use Vagrant, then
might as well get the provisioning script to do that as well.

A nice side-effect is that, if the Vagrant box was brought up OK,
all the tests pass immediately.
Updated README

I took out the instructions to run the application locally, as I
imagine any developer who wants to deviate from the Vagrant
install will know how to do that (or follow the Vagrant.sh script
as a rough guide).