Improve label picking (#1179)

* add simple error message helper

* port all label name pickers to use the new LabelInput component

* use pure components where possible

* cleanup

* more cleanup

* lint

* change new label prompt

client/src/reducers/categoricalSelection.js

@@ -1,5 +1,4 @@
 import { ControlsHelpers as CH } from "../util/stateManager";
-import * as globals from "../globals";
 
 const CategoricalSelection = (
   state,