Add ability to toggle visibility of the footer opt out link.
Merge pull request #627 from moneyadviceservice/footer-opt-out

Add ability to toggle visibility of the footer opt out link
Update Rails to 4.1.5
Add test for error view
Bump pensions calculator.
A set of classes to encapsulate details for mounting engines.

Setup for our first engine, pensions calculator, with a pattern that can be expanded for other engines.
Implement the language translation link and alternate meta tags for engines.
Implement correct constraints for the pensions calculator.