Extensible select and enumeration types

and their elements in schema Scheme_arm taking into account BASED_ON types


 activity_method_item - EXTENSIBLE GENERIC_ENTITY SELECT

 date_or_date_time_item - EXTENSIBLE SELECT
          Scheme_entry

 measure_value - EXTENSIBLE SELECT
          any_number_value
          any_string_value
          length_measure
          plane_angle_measure

 organization_or_person_in_organization_item - EXTENSIBLE SELECT
          Scheme
          Scheme_entry