Update UI through async calls MainFrameRepaint and AddressBookRepaint instead of a timer.

- Overall, this is better design
- This fixes problems with the address book UI not updating when the address book is changed through RPC
- Move Statusbar change detection responsibility to ClientModel

src/qt/walletmodel.h

@@ -138,9 +138,8 @@ signals:
     void error(const QString &title, const QString &message);
 
 public slots:
-
-private slots:
     void update();
+    void updateAddressList();
 };