[Qt] add ui signal for banlist changes

src/ui_interface.h

@@ -95,6 +95,9 @@ public:
 
     /** New block has been accepted */
     boost::signals2::signal<void (const uint256& hash)> NotifyBlockTip;
+
+    /** Banlist did change. */
+    boost::signals2::signal<void (void)> BannedListChanged;
 };
 
 extern CClientUIInterface uiInterface;