validate reserved names in set_properties

reset enum_values to None when last value deleted

validate duplicate names in set_properties

validate reserved names in property rename

reject duplicate names and shortcuts in set_statuses

fix get_parameter returning None for absent style

reject duplicate enum value name in add_enum_property

fix property rename to same name deleting task data

reject duplicate shortcut in add_status

fix task_edit id deleting task when id unchanged

fix update_task_id deleting task when id unchanged

fix panic in get_text_from_editor when editor fails

reject duplicate property name in add_property

reject duplicate status name in add_status

fix get_starting_status panic on empty statuses