Apply validation errors conditionally depending on whether is 1st or 2nd person.
Add validation messages to step 3.
Refactor/tweak validations so they raise all the right messages and none of the wrong ones.
Add specs for Person -> Affordability relationship.
Merge pull request #214 from moneyadviceservice/fix_failing_tests

Fix failing tests
Accessibility adjustments.

* Add instructions to input-field-with-slider and hide the slider for screen readers.
* Add explicit information on functionality to a click-to-expand link.
* Swap left and right panels to make markup order friendlier to screen reader navigation.
Restructure headings to produce correct order for accessibility purposes.

i.e. h1 -> h2 -> h3.
Add Welsh translation.