Enumerations: courseMode <CourseMode>, courseDigitalFormat <CourseDigitalFormat>, accessibilityPhysicalFeature <AccessibilityPhysicalFeature>

In reading the examples that Phil added here:
https://github.com/westurner/schemaorg/pull/3#issuecomment-220782903

I wonder whether, for faceted interface support, we should have courseMode
Enumerations?

We could define said Enumerations just like these:
https://www.w3.org/wiki/WebSchemas/Accessibility


AccessibilityPhysicalFeature (for Place, Event, CreativeWork, )
https://www.w3.org/wiki/WebSchemas/Accessibility PhysicalFeature
- name
- description
- url
- image / logo / photo (Creative Commons {SVGs,} would be great here)
- https://github.com/schemaorg/schemaorg/pull/972#issuecomment-173698449


CourseMode
https://www.w3.org/wiki/WebSchemas/CourseMode
- name
- description
- url


CourseDigitalFormat
https://www.w3.org/wiki/WebSchemas/CourseDigitalFormat
- name
- version
- description
- url


Suggestions:
- These Enumeration URLs should/could be copy-paste-able
- Semantic MediaWiki supports RDFa
  - IDK how feasible it would be to get W3C support for Semantic MediaWiki
(or really who to contact for such a request)