Create v4.2 of the page flow

[simonwhatley]

This PR creates version 4.2 of the page flow.

View prototype: https://lung-health-check-pr-87.herokuapp.com/prototype_v4_2/start-page

Changes:

• Reorganised the page flow to be:
  • eligibility
  • about you
  • smoking history
  • your health
  • your family history
• Combined questions on a single page, for example:
  • smoking frequency and quantity
  • age started, aged quit, periods stopped
  • asbestos
• Reworded some questions (to be consistent with some of the 4.3 pages)
• Updated the docs including flow diagram