Enable modifying a caseload, but keeping most of its resultant schedule the same

Right now, there's no easy way to modify *part* of a schedule result. This is useful when a student gets added to a caseload the 4th week of school.

This can be done by adding a button that converts current results to Exact Spans in the caseload. Then, the therapist can make changes or delete Exact Spans as necessary. When run again, the engine will keep all of the results with a single Exact Span, leaving the majority of the schedule result intact.