modified form validation rules to comply with AAMC business rules for session blocks representing clerkship courses. refs #3782
fixed bug that was causing sequence blocks to lose state for courses after repeated updates when courses did not change.
fixed minor regression in updating a sequence block with a previous unselected course association.
fixed another edge case related to updating the course selection in sequence blocks.
Merge pull request #179 from ilios/rb2.3

reintegrate release branch rb2.3 into master