Make state pension calculator stateless

The fact that the state pension calculator was keeping retirement
age as part of its state was causing erroneous calculations for people around
male or female retirement age.
Merge pull request #1321 from alphagov/not-all-men-state-pension

Make state pension calculator stateless
Minor copy updates to check-uk-visa smart-answers (v2)

Adding small piece of markdown (twice) and swapping out a bullet point that was missed by FCO.
Remove clickbooks links
The service that allowed to book appointments at embassies and consulates is not active anymore. I removed every reference to it from Register a Birth and Register a Death Smartanswers
Merge pull request #1320 from alphagov/remove_clickbooks_register_a_birth_and_death

Remove clickbooks from register a birth and death
Updating copy for check-uk-visa smart-answer (v2)

More small changes and a bit of tidying up.
Merge pull request #1322 from alphagov/more_minor_updates_to_ukvisa

Updating copy for check-uk-visa smart-answer (v2)