Fix to previous answers css

- Previous answers block width now follows width of current questions above.
- With long previous questions the block no longer expands to far to the right.

The local static media-down mixin is the local conditionals2 which static uses. It is only here for a short time until the forking of the smart answers css is completed.

https://www.agileplannerapp.com/boards/105200/cards/5834
Change v2 files to v1
Merge pull request #1148 from alphagov/fix-previous-answers-table-width

Fix to previous answers css
Adjust leap year birthday forward by one day

- For birthdays which fall on the 29th February in a leap year the calculator shifts their birthday to the 1st March for the purposes of finding the correct rate.
- This is similar to what the calculate-state-pension tool does.
Merge pull request #1153 from alphagov/fix-errbit-error-state-pension-topup

Fix errbit error state pension topup