* add several methods to the sales log to allow subsequent work to be human readable
* add a validation to prevent an inconsistent combination of values and tests for this validation
* handle derivation of values around buyers living in the property
- derive values where appropriate
- clear these values when the derived state no longer holds
- update the routing for pages holding questions about whether particular buyers will live in the property to reflect when they are derived
- test the deriving and associated clearing of values
- update tests on page routing and sales log factory
* update a page routing condition for human readability using an existing method and update test to reflect this change
* show related method in diff
* minor amendments after tech review
* simplify reset_derived_questions after tech review
* refactor on deriving and clearing invalid derived values on sales log
* correct linter complaints
* remove comment
* add validation to one more field with a new error message as it is in fact possible to tirgger the validation in the setup section
Arthur Campbell