qt: Show progress overlay when clicking spinner icon

Bring up the modal progress overlay when the user clicks the spinner
icon in the task bar.

I think this is the intuitive thing to do when that icon is clicked.

src/qt/bitcoingui.cpp

@@ -200,7 +200,7 @@ BitcoinGUI::BitcoinGUI(const PlatformStyle *_platformStyle, const NetworkStyle *
     labelWalletEncryptionIcon = new QLabel();
     labelWalletHDStatusIcon = new QLabel();
     connectionsControl = new GUIUtil::ClickableLabel();
-    labelBlocksIcon = new QLabel();
+    labelBlocksIcon = new GUIUtil::ClickableLabel();
     if(enableWallet)
     {
         frameBlocksLayout->addStretch();
@@ -248,8 +248,10 @@ BitcoinGUI::BitcoinGUI(const PlatformStyle *_platformStyle, const NetworkStyle *
 
     modalOverlay = new ModalOverlay(this->centralWidget());
 #ifdef ENABLE_WALLET
-    if(enableWallet)
+    if(enableWallet) {
         connect(walletFrame, SIGNAL(requestedSyncWarningInfo()), this, SLOT(showModalOverlay()));
+        connect(labelBlocksIcon, SIGNAL(clicked(QPoint)), this, SLOT(showModalOverlay()));
+    }
 #endif
 }