Merge pull request #132 from force-h2020/feature/re-export-factory_id-0518-1133

Exports factory_id as we need it when two factories need to find each other.

force_bdss/api.py

 from .base_extension_plugin import BaseExtensionPlugin  # noqa
-from .ids import plugin_id  # noqa
+from .ids import plugin_id, factory_id  # noqa
 
 from .core.data_value import DataValue  # noqa
 from .core.workflow import Workflow  # noqa