- specify default datetime columns so that "added_on" and "chng_on" are automatically converted to timestamp columns.
- specify surface_date as a date column in the TopSurface class definition.
- add a from_frame method to the BaseTable class. The method converts datetime columns and sets the dataframe index as per the table definition. A step has been added to the top_surface ops functions to make sure the dataframe arguments are formated correctly.