Clarify relationship of Associated material to Learning Components

[philbarker]

e.g. statement that "A Lesson contains instructional content intended to be completed in a single day or class period" is misleading if AssociatedContent is integral part of lesson CCM type.

Better: "A Lesson in OCX is instructional content and associated material that represents a learning experiences that can be completed in a single day or class period"

ocx:material refines schema.org:hasPart to be the part of a Lesson in OCX that that teaches the content of the lesson, is referenced by the content of the lesson or provides further information about the content of the lesson.

Alternatively a lesson is a learning experience, and LessonPlans are resources that can be used to create a lesson. In which case material is how we associate LessonPlans to Lessons.