allow course group priorities for applying credits toward degree audit

We have many courses that appear in more than one course group. We would like to be able to indicate a relative priority for which course group to apply credits to. We can manually review the audits, but when a course group is edited, for example if a new course is created it appears to reset (and scramble) where these courses are applied. In particular, we would like to deprioritize a specific course group that more or less contains all the course in our program (an elective group where students can fill out their studies according to their interests.)