SDAC - Update the fragility model db schema to support the noDamageLimit attribute (and related writers)

[Giuseppe Vallarelli]

In order to support the noDamageLimit attribute in the fragility models. We need to update the db schema by adding a new attribute to riski_fragility_model table (see https://github.com/gvallarelli/oq-engine/blob/master/openquake/db/schema/openquake.sql#L1627) as well as the related model (see https://github.com/gvallarelli/oq-engine/blob/master/openquake/db/models.py#L1441) and the writer (see https://github.com/gvallarelli/oq-engine/blob/master/openquake/input/fragility.py#L29).