Added more comments

src/app/core/submission/models/workflowitem.model.ts

 import { Workspaceitem } from './workspaceitem.model';
 
+/**
+ * A model class for a Workflowitem.
+ */
 export class Workflowitem extends Workspaceitem {
 }

src/app/core/submission/models/workspaceitem.model.ts

 import { SubmissionObject } from './submission-object.model';
 
+/**
+ * A model class for a Workspaceitem.
+ */
 export class Workspaceitem extends SubmissionObject {
 
 }