Clean up Vagrant provisioning config.

Made a few adjustments so less network is used (and more is logged
while the script is at it, for those often on crappy airport wifi
networks like me :)

Additionally, the script is mostly idempotent now, so that if you
run `vagrant provision` again, it shouldn't blow up or do anything
unwanted.
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).
Fix some typos and use better sentence structures.
Bring back the local install instructions
Formatting and making sure lines are not so long.
Merge pull request #15 from cv/vagrant-cleanup

Clean up Vagrant provisioning config.