Finished second update of mass migrations.

Added missed constants.

Added common function used by alembic to handle nullabel=False.

Fixed alembic downgrade issues.

Reflected in migrations ElemPath to JSONPointer replacement.

Working on migrations.

Working on migrations.

Working on alembic migrations.

Finished second pahse of mass migration.

Renamed migration 0015 to 0014.

Changed alembic id in migration 0014.