Don't store answers for no answer activities

Problem/Motivation

Some activities (currently only the "no answer" one but there can potentially be more) don't store any answer data and are basically read-only. We shouldn't need to store answer entities for them.

Proposed resolution

Don't store answer entities for activities with answer plugins that don't store data.
Update Drupal\lms\TrainingManager::updateLessonStatus() to account for that. If possible, don't instantiate all the answer plugins to check but have that information stored in their definitions instead.