Add default file viewer

moneymgr_web/src/api/FileApi.ts

@@ -37,4 +37,11 @@ export class FileApi {
       })
     ).data;
   }
+
+  /**
+   * Get a file download URL
+   */
+  static DownloadURL(file: UploadedFile): string {
+    return APIClient.backendURL() + `/file/${file.id}/download`;
+  }
 }