Married couple's allowance - April 6 changes

Updates to a published smartanswer for April 6th. Don't merge yet.
Make April 6th changes be done through Timecop

This makes the April 6th changes happen automatically, and doesn't rely
on us doing a midnight deploy or anything like that.
Change smart quote to single apostrophe
Merge pull request #262 from alphagov/calculate-married-couples-allowance

Married couple's allowance - April 6 changes