Set 'istate_status_names' and 'istate_type_names' class attributes. (#258)
Set 'istate_status_names' and 'istate_type_names' class attributes. (#258)

* Set 'istate_status_names' and 'istate_type_names' class attributes.

* Add 'ISTATE_xxxx_' prefix to InitialState.istate_xxxx_names.

* Apply black.
westpa/westpa