Remove development_no_vm configuration

This doesn't do anything that you couldn't do by adding a single
host entry for spotlight.perfplat.dev and using the development
config.
Add ability to use a gitignored config in dev

This is nice if you like to use preview or production data regularly
in development.

Also massively update the README.
Merge pull request #204 from alphagov/better-dev-config

Better dev config