Don't delete dataset in DB when annotations exist

frontend/javascripts/dashboard/advanced_dataset/dataset_action_view.tsx

@@ -169,7 +169,17 @@ class DatasetActionView extends React.PureComponent<Props, State> {
           onClick={() =>
             Modal.error({
               title: "Cannot load this dataset",
-              content: dataset.status,
+              content: (
+                <div>
+                  <p>{dataset.status}</p>
+                  {dataset.status === "Deleted by user." ? (
+                    <p>
+                      Even though, this dataset was deleted by a user, it is still shown here,
+                      because it is referenced by at least one annotation.
+                    </p>
+                  ) : null}
+                </div>
+              ),
             })
           }
         >

frontend/javascripts/dashboard/dataset/dataset_settings_delete_tab.tsx

@@ -34,7 +34,7 @@ const DatasetSettingsDeleteTab = ({ datasetId, history }: Props) => {
     }
 
     const deleteDataset = await confirmAsync({
-      title: `Deleting a dataset on disk cannot be undone. Are you certain to delete dataset ${dataset.name}?`,
+      title: `Deleting a dataset on disk cannot be undone. Are you certain to delete dataset ${dataset.name}? Note that the name of a dataset is not guaranteed to be free to use afterwards.`,
       okText: "Yes, Delete Dataset on Disk now",
     });