update _global_redshift

* needed for new lines to immediately adopt the current redshift
* redundancy between self.rs_redshift and _global_redshift seems to exist for future flexibility of allowing multiple redshifts - but if that is ever abandoned, we should merge and replace all instance of _global_redshift with rs_redshift

jdaviz/configs/default/plugins/line_lists/line_lists.py

@@ -208,6 +208,8 @@ def _on_rs_redshift_updated(self, event):
                 # so we'll just leave empty
                 return
             value = float(event['new'])
+            # update _global_redshift so new lines, etc, will adopt this latest value
+            self._global_redshift = value
             self._rs_disable_observe = True
             self.rs_rv = self._redshift_to_velocity(value)
             self._rs_disable_observe = False