NPM harness

I had some problems running the build because my global plumber is incompatible.  Wrapping the test and build tasks with npm uses the local binaries which removes the issue. Ive also wrapped the setup.sh into a post install which means you only have to execute npm install to get up and running.
Parameterise BROWSER_NAME here, even though Firefox is broken locally at the moment we shouldn't enshrine that.