🌐 Search engine custom button

public/locales/en/settings/general/search-engine.json

@@ -1,6 +1,7 @@
 {
   "title": "Search engine",
   "configurationName": "Search engine configuration",
+  "custom": "Custom",
   "tips": {
     "generalTip": "There are multiple prefixes you can use! Adding these in front of your query will filter the results. !s (Web), !t (Torrents), !y (YouTube), and !m (Media).",
     "placeholderTip": "%s can be used as a placeholder for the query."