When users join or leave review groups, their incoming review request

counter retains its older value, leading to discrepencies that only get

fixed with resetting that counter on their profile. This is an old bug,

which oddly we haven't heard anything about (at least directly -- it may

have been the unknown cause of some bug reports in the past).
We now listen for membership changes on groups and perform a reset on

any profiles that may exist that pertain to the users involved in the

change. This clears out the counter, which is fast, causing it to be

recalculated the next time it's loaded.
This works whether a user changes their own membership or an admin

bulk-modifies the membership on a group through the Admin UI.

Unit tests pass.