Use govuk.buildProject in Jenkinsfile
Use govuk.buildProject in Jenkinsfile

As far as I can tell this previously followed the steps for
govuk.buildProject() almost exactly (but a bit out of date).

There's a bunch of work to be done to get the sass linting to play ball
though so this has been disabled.

alphagov/signonotron2,alphagov/signonotron2,alphagov/signonotron2,alphagov/signonotron2