several small Qt-related fixes

- make BitcoinGUI::showPaymentACK() use a reference for msg and use our
  own GUIUtil::HtmlEscape() function
- ensure QTimer usage in clientmodel is the same as in walletmodel
- remove an unneeded debug message in walletframe
- flag some parameters as unused in DebugMessageHandler()
- small code formatting changes

src/qt/clientmodel.cpp

@@ -24,9 +24,8 @@ ClientModel::ClientModel(OptionsModel *optionsModel, QObject *parent) :
     numBlocksAtStartup(-1), pollTimer(0)
 {
     pollTimer = new QTimer(this);
-    pollTimer->setInterval(MODEL_UPDATE_DELAY);
-    pollTimer->start();
     connect(pollTimer, SIGNAL(timeout()), this, SLOT(updateTimer()));
+    pollTimer->start(MODEL_UPDATE_DELAY);
 
     subscribeToCoreSignals();
 }