Add function to open a link

- Does not seem to actually ... work.. yet

lib/widget/category_display.dart

@@ -267,6 +267,7 @@ class PartList extends StatelessWidget {
     return ListTile(
       title: Text("${part.name}"),
       subtitle: Text("${part.description}"),
+      trailing: Text("${part.inStock}"),
       leading: InvenTreeAPI().getImage(
         part.thumbnail,
         width: 40,