Add list duplicate (#172)

Add list duplicate

Co-authored-by: kolaente <k@knt.li>
Reviewed-on: https://kolaente.dev/vikunja/frontend/pulls/172

src/models/listDuplicateModel.js

@@ -0,0 +1,17 @@
+import AbstractModel from './abstractModel'
+import ListModel from './list'
+
+export default class ListDuplicateModel extends AbstractModel {
+	constructor(data) {
+		super(data)
+		this.list = new ListModel(this.list)
+	}
+
+	defaults() {
+		return {
+			listId: 0,
+			namespaceId: 0,
+			list: ListModel,
+		}
+	}
+}