Drop need for change events in property configurers

[mike-hogan]

Events were settled on to enable sql schema migrations, but they have been binned.

Events are still nice for history and undo etc.

But can we keep the best of both worlds by either:

1. Providing the property as a Writable to the Configurer, and subscribing to changes
2. Using something like valtio to achieve the same

[mike-hogan]

https://www.npmjs.com/package/on-change

[mike-hogan]

Done