make more _ermrest schema constraints DEFERRABLE to help with dump/restore
make more _ermrest schema constraints DEFERRABLE to help with dump/restore

When revising the stateful model en masse to resynchronize OIDs after
a dump/restore, some constraints could have conflicts depending on
partial overlaps between the OID range of source and destination
postgres databases.

This fix is only for new catalogs. Existing dumps may need manual
intervention to drop and recreate constraints if
_ermrest.model_change_event() fails on constraint violations due
to this underlying scenario.

informatics-isi-edu/ermrest,informatics-isi-edu/ermrest