ISIS-776: further improvements to fixture script API

Only view models or already persisted objects can be added to a FixtureResultList.  FixtureScripts can now be configured with a NonPersistedObjectsStrategy whereby it will either ignore or auto-persist any objects added to a fixture result that are not yet persisted.
ISIS-776: either autoComplete or choices for fixture script drop-down.
ISIS-782: install FixtureClock in IsisSystemForTest