Merge pull request #169 from force-h2020/base-factory-api

Add BaseFactory to API

force_bdss/api.py

 from .base_extension_plugin import BaseExtensionPlugin  # noqa
 from .ids import plugin_id, factory_id  # noqa
 
+from .core.base_factory import BaseFactory  # noqa
 from .core.data_value import DataValue  # noqa
 from .core.workflow import Workflow  # noqa
 from .core.slot import Slot  # noqa