Search improvements (#388)

* Refactor search widget

- visual improvements
- Simplifications
- Add refresh button
- Improve search button

* Track original search

* fix BOM widget

* Update release notes

lib/inventree/stock.dart

@@ -117,7 +117,16 @@ class InvenTreeStockItemHistory extends InvenTreeModel {
     }
   }
 
-  String get userString => getString("username", subKey: "user_detail");
+  int? get user => getValue("user") as int?;
+
+  String get userString {
+
+    if (user != null) {
+      return getString("username", subKey: "user_detail");
+    } else {
+      return "";
+    }
+  }
 }