Add general purpose support for predicate union (or)

aliased to `|`.
Update overseas-passports to use next_node_if

also refactored to use predicates which generate helpful labels
Convert maternity-paternity-calculator.rb to next_node_if
Convert register-a-birth to #next_node_if
Refactor register-a-death to use next_node_if
Update register a birth and death V2 flows

- Updated next node in flows
- Additional methods in registrations data query
Merge pull request #904 from alphagov/static-next-node-step2

Convert another batch of smart answers to use new next_node syntax