Allow manually adding a class that's already been added by a worker

vue/Element/DetailsPanel.vue

@@ -153,7 +153,7 @@ export default {
       return this.selectedNewClassification &&
         this.element &&
         this.element.classifications &&
-        this.element.classifications.find(c => c.ml_class.id === this.selectedNewClassification)
+        this.element.classifications.find(c => (c.ml_class.id === this.selectedNewClassification && !c.worker_version))
     },
     canCreateClassification () {
       return this.element && this.selectedNewClassification && !this.manualClassificationExists && !this.isSavingNewClassification