Updating the studio mixin to deliver context with initial rendering

* Removed CodeMirror (just text fields now)
* Changed collapse / expand to use the is--hidden toggled class for assessments
* Broke oa_edit.html into several templates (this will help with drag and drop)
* Ripped everything out of oa_edit.js load()

Some things still broken:
* Certain buttons / listeners are not wired where they were in the load() function
* Save is not working due to criteria count in the Rubric

If this condition occurs, the template will still get rendered, but `assessments['training']` might not be set.  Will this lead to unexpected behavior?