Update state pension calculator logic and content

- Added 2 new questions to flow.
- Adjusted logic for outcomes.
- Change in content for questions and some outcomes.
- Adjusted tests for coverage of new flow and logic.
- Fixed leap year bug which was showing an extra day in the age output for those born on the 29th Feb in a leap year.

https://www.pivotaltracker.com/story/show/73306102
Not quite sure what FriendlyTimeDiffV2. Could we have a more descriptive name, or some kind of description of what it does as a comment if there is no way of renaming this?