Simplify secondary footer language

We don’t have screen real-estate to be so wordy.
Add newsletter form translations
Marking up newsletter subscription
Add contact us link to primary footer
Remove placeholder in the newsletter input box
Reduce font size of the footer-secondary elements
Merge pull request #601 from moneyadviceservice/footer_bugs

Footer bugs
Add class to all language links
Merge pull request #600 from moneyadviceservice/language_link_fix

Add class to all language links
Fix for newsletter input height
Bump pensions calculator.
Change MQ for footer to fix wrapping bug
Fix failure for link to underline on promo boxes
Allow heading tag helper to accept optional attrs
Allow heading tag helper to accept optional block
Apply accessible headings to views
Add accessible headings to the content
ActionPlanDecorator is a ContentItemDecorator

Allows ActionPlanDecorator to inherit the default html_processors that are common for all the content decorators
ActionPlanDecorator keeps the right aria-level value
NewsArticleDecorator uses the inherit html processors