Improve HK sidebar and restore nested content scrolling

src/messages/en.json

@@ -1058,6 +1058,9 @@
 				"backToSite": "Back to site",
 				"expandAll": "Expand all",
 				"collapseAll": "Collapse all",
+				"searchMenu": "Search menu…",
+				"clearMenuSearch": "Clear menu search",
+				"noMenuResults": "No matching pages.",
 				"housekeeping": "Permission archive",
 				"hotelManagementPanel": "Hotel management panel",
 				"rankLabel": "Rank {rank}",