WebUI: Add multi-file renaming

PR #18287.
Closes #16239.

src/webui/www/private/scripts/preferences.js

@@ -54,6 +54,15 @@ window.qBittorrent.LocalPreferences = (function() {
             catch (err) {
                 console.error(err);
             }
+        },
+
+        remove: function(key) {
+            try {
+                localStorage.removeItem(key);
+            }
+            catch (err) {
+                console.error(err);
+            }
         }
     });