Consequences of changing configuration

@cahrens , @explorerleslie , @gwprice , @zhkramer , @srpearce : last big chunk, let me know what I've gotten wrong and what I've forgotten!
I'm going to leave the two sections for renaming (and deleting) a cohort group with their current headings, as I think that course authors will be thinking in those terms when they look up info, rather than in terms of what setting or UI control they're working with. On the other hand, you're all right about how wishy-washy the lead-in was about making changes to auto cohort groups, so I strengthened/changed the wording about what you think you're doing vs. what you're actually doing. 
The load rebalancing info is super useful.
Addressed.