Parse flow only once
Merge pull request #1146 from alphagov/performance

Parse flow only once
Tentative performance change
Flow combination generator
Fix errors in flow
Fix errors and single parent birth flows
Remove all pending cases from birth flows
Remove all TODOs from flow
Human-readable and machine-readable factcheck scenarios
Correct last invalid snippet keys
Correct snippet syntax
Add SPL snippets
Add TODO plugins and additional snippets with correct variable use
Clean up commits
Update of the content document
Scenarios and factcheck in separate objects, better errors, newlines for scenarios