Add empty initialisation for models

Created by: stefanoborini

Allows for models to be initialised without JSON data, but just from the default content (traits instantiation)

force_bdss/core_plugins/csv_extractor/csv_extractor/csv_extractor_model.py

-from traits.api import HasStrictTraits, Int, String
+from traits.api import Int, String
 
+from force_bdss.data_sources.base_data_source_model import BaseDataSourceModel
 
-class CSVExtractorModel(HasStrictTraits):
+
+class CSVExtractorModel(BaseDataSourceModel):
     filename = String()
     row = Int()
     column = Int()