Add translation for "Show desktop drag handles".

Thanks to xet7 !

i18n/en.i18n.json

@@ -738,5 +738,6 @@
   "act-atUserComment": "You were mentioned in [__board__] __card__",
   "delete-user-confirm-popup": "Are you sure you want to delete this account? There is no undo.",
   "accounts-allowUserDelete": "Allow users to self delete their account",
-  "hide-minicard-label-text": "Hide minicard label text"
+  "hide-minicard-label-text": "Hide minicard label text",
+  "show-desktop-drag-handles": "Show desktop drag handles"
 }