Sample course: assessment article trickle missing _onChildren

[swashbuck]

Subject of the enhancement

In the sample course, there is an assessment on the a-300 article. Trickle is enabled here, but the _onChildren property is not explicitly set. When not included on an article's _trickle, _onChildren behaves as if set to true and child blocks are locked one by one. Oddly, the schema defaults to false which seems to be counterintuitive.

Due to this, a problem can occur when importing a framework course into the AAT as the _onChildren value will be set to false after import. This causes a discrepancy since the course developer expects Trickle to function as it does in the framework. While not a breaking issue by any means, it can require additional troubleshooting time.

TL;DR: I suggest adding "_onChildren": true to the a-300 article's _trickle settings.