homework: don't try to shift uidmap for already activated home areas

homework: don't try to shift uidmap for already activated home areas

When we want to operate on an already activated home area we so far
tried to reapply the uidmapping logic. We shouldn't do that, it's
already applied after all.

We only want to apply this for newly activated home areas. Hence check
for the right HomeSetupFlags flag for it HOME_SETUP_ALREADY_ACTIVATED.

The patch is actually in theory a two-liner. Except that so far we don#t
pass the HomeSetupFlags flags down all necessary functions where the
uidmap stuff will eventually run. Hence this larger than intended
commit.