Introduces fast declaration style for factory

Created by: stefanoborini

Makes it faster to define the factory by specifying just the class, factoring out the boilerplate of the reimplementation of the method.

This is backward compatible with the current plugins

force_bdss/data_sources/base_data_source.py

-from traits.api import ABCHasStrictTraits, Instance
 import abc
+from traits.api import ABCHasStrictTraits, Instance
 
 from ..data_sources.i_data_source_factory import IDataSourceFactory