Creating a sectionGroup for a course with existing TeachingAssignments does not clone the TeachingAssignments appropriately

[cthielen]

Our current design requires that if new section groups are created (say, a 'B' series being added in addition to an 'A' series) on courses that already have TeachingAssignments (which may be preferences) for that course, we need to clone the TeachingAssignments as well.

We should fix this bug in the near future, and correct this design flaw of needing to clone something in the future.