Add scripts to run jenkins builds and branch builds

Conforms to similar projects we have that build against branches and
directly for master.
Merge pull request #3 from alphagov/add-jenkins-and-branch-build-scripts

Add scripts to run jenkins builds and branch builds
Add slimmer to get header, footer, report-a-problem
Add rspec
Failing spec for viewing the need for a given slug
Start integration with metadata-api

This includes a hack (that will be refactored later) to include
the `govuk-client-url_arbiter` gem (so that we can reuse the JSON
client).
Render needs on the info page
GOV.UK rendering and styling of info page
Better signposting for the needs on the info page
Extend spec coverage

Spec now covers need acceptance criteria and justification
Info page: handle slugs without needs