AnyRsetView: Refactor the columns_name method and update doc. We drop the 'label_column_%s' % colidx pattern and add a clean column_label method that might be overwritten by children class to alter the way default columns headers are computed.

if schema['TZDatetime'].eid is None:
    add_entity_type('TZDatetime')
if schema['TZTime'].eid is None:
    add_entity_type('TZTime')