allow emit message() in sendcoinsdialog and walletview

- this allows us to use emit message() over MessageBox:: or gui->message()
  calls in sendcoinsdialog and walletview
- move main handlePaymentRequest() functionality back to BitcoinGUI
- move a showNormalIfMinimized() before gotoSendCoinsPage()

src/qt/sendcoinsdialog.h

@@ -52,6 +52,10 @@ private slots:
     void on_sendButton_clicked();
     void removeEntry(SendCoinsEntry* entry);
     void updateDisplayUnit();
+
+signals:
+    // Fired when a message should be reported to the user
+    void message(const QString &title, const QString &message, unsigned int style);
 };
 
 #endif // SENDCOINSDIALOG_H