ok, so the estate stores now want their own migration files, but as it
happened the SQL definition were inside the Region migrations.
It seems better/cleaner to keep each 'store' separately updatable.
WARNING: any editing in the middle of the migration scripts (as opposite
to just appending to them) has the potential of messing up updates of
existing databases. As far as I can see, this one is (probably) safe,
the worst that could happen is the EstateStore migration silently fail
if the estate the tables are already there.
