agile: update Add diff support
diagrams: refactor SML diagram has it has gotten pretty messy
agile: add spikes and update clocks for sprint 26
agile: update Create a validator in SML
agile: update Create a validator in SML
stereotypes: add aggregate root scenario

- implement remaining functionality needed to support aggregate root
  scenario
- add tests for it
sml: add aggregate roots and other minor tidy-ups