Bitcoin-Qt: add "send coins" to context menu in addressbook

- allows to directly select an address from the addressbook, chose "send
  coins" from the context menu, which sends you to sendcoins tab and fills
  in the selected address

src/qt/bitcoingui.h

@@ -149,7 +149,7 @@ private slots:
     /** Switch to receive coins page */
     void gotoReceiveCoinsPage();
     /** Switch to send coins page */
-    void gotoSendCoinsPage();
+    void gotoSendCoinsPage(QString addr = "");
 
     /** Show Sign/Verify Message dialog and switch to sign message tab */
     void gotoSignMessageTab(QString addr = "");