Only load Google Tag Manager in production

This stops red builds caused by rogue JS provided by the GTM config.
Remove authentication feature toggle
Add Car Costs Calculator CTA to car campaign page
Merge branch 'cta-car-campaign'
Add active categories to action plans
Merge branch 'bug/action-plan-lef-navigation'
Add rel attributes to news pagination
Merge branch 'pagination-rel-attributes'
Add description meta tag to news index
Merge branch 'news-index-description'
Fix GTM
Convert newsletter input to text_field from email_field
Add fieldset around form and replace h2 with legend
Make some accessibility improvements to the newsletter form JS

Add aria-invalid, aria-describedby to newsletter input and role=alert
for thank you message …and some other code tidies.
Update Sass comment
Convert hard coded ID into variable on Newsletter signup JS
Fix car campaign and menu item alignments
Merge pull request #543 from moneyadviceservice/ui_fixes

Fix car campaign and menu item alignments
Revert "Remove block from news reader"

This reverts commit af13d46eba4c96f465ac171864b4b1b11bcdb88a.
Call block when repository returns an empty collection