A first pass at containers.

Restructred the container to be heavily reliant on DOM structure,
largely ignoring all unique identifiers and shrinking the implicit size
of the Container Item classes

Completed the initial pass of the Container Item Class.

Added tests and fixed major and minor issues.

Conflicts:
	openassessment/xblock/static/js/openassessment.min.js
Checkpoint -- integrating containers into the rubric view