Add field validation for datetime fields and option points.
Remove support in Javascript for "default" (empty) dates and update the template rendering script to support this in the JS tests.
Merge branch 'will/js-field-validation' of https://github.com/edx/edx-ora2 into grady/js-validation-alert-broadening

Conflicts:
	openassessment/xblock/static/js/openassessment-studio.min.js
	openassessment/xblock/static/js/src/studio/oa_container_item.js
	openassessment/xblock/static/js/src/studio/oa_edit.js
	openassessment/xblock/static/js/src/studio/oa_edit_assessment.js
	openassessment/xblock/static/js/src/studio/oa_edit_fields.js
	openassessment/xblock/static/js/src/studio/oa_edit_rubric.js
	openassessment/xblock/static/js/src/studio/oa_edit_settings.js
	openassessment/xblock/static/js/src/studio/oa_edit_validation_alert.js
	scripts/render_templates.py