Disable the main window toolbar when the modal overlay is shown

Summary:
> qt, refactor: Cleanup ModalOverlay slots

> qt: Disable toolbar when overlay is shown

This is a backport of [[bitcoin-core/gui#30 | core-gui#30]]

Test Plan: `bitcoin-qt --regtest

Reviewers: #bitcoin_abc, majcosta

Reviewed By: #bitcoin_abc, majcosta

Differential Revision: https://reviews.bitcoinabc.org/D9994

Author: hebasto

src/qt/bitcoingui.cpp

@@ -110,6 +110,8 @@ BitcoinGUI::BitcoinGUI(interfaces::Node &node, const Config *configIn,
         Q_EMIT consoleShown(rpcConsole);
     }
 
+    modalOverlay = new ModalOverlay(enableWallet, this->centralWidget());
+
     // Accept D&D of URIs
     setAcceptDrops(true);
 
@@ -203,7 +205,6 @@ BitcoinGUI::BitcoinGUI(interfaces::Node &node, const Config *configIn,
     connect(labelProxyIcon, &GUIUtil::ClickableLabel::clicked,
             [this] { openOptionsDialogWithTab(OptionsDialog::TAB_NETWORK); });
 
-    modalOverlay = new ModalOverlay(enableWallet, this->centralWidget());
     connect(labelBlocksIcon, &GUIUtil::ClickableLabel::clicked, this,
             &BitcoinGUI::showModalOverlay);
     connect(progressBar, &GUIUtil::ClickableProgressBar::clicked, this,
@@ -243,6 +244,8 @@ BitcoinGUI::~BitcoinGUI() {
 
 void BitcoinGUI::createActions() {
     QActionGroup *tabGroup = new QActionGroup(this);
+    connect(modalOverlay, &ModalOverlay::triggered, tabGroup,
+            &QActionGroup::setEnabled);
 
     overviewAction =
         new QAction(platformStyle->SingleColorIcon(":/icons/overview"),

src/qt/modaloverlay.cpp

@@ -190,6 +190,8 @@ void ModalOverlay::showHide(bool hide, bool userRequested) {
         return;
     }
 
+    Q_EMIT triggered(hide);
+
     if (!isVisible() && !hide) {
         setVisible(true);
     }

src/qt/modaloverlay.h

@@ -25,17 +25,21 @@ class ModalOverlay : public QWidget {
     explicit ModalOverlay(bool enable_wallet, QWidget *parent);
     ~ModalOverlay();
 
-public Q_SLOTS:
     void tipUpdate(int count, const QDateTime &blockDate,
                    double nVerificationProgress);
     void setKnownBestHeight(int count, const QDateTime &blockDate);
 
-    void toggleVisibility();
     // will show or hide the modal layer
     void showHide(bool hide = false, bool userRequested = false);
-    void closeClicked();
     bool isLayerVisible() const { return layerIsVisible; }
 
+public Q_SLOTS:
+    void toggleVisibility();
+    void closeClicked();
+
+Q_SIGNALS:
+    void triggered(bool hidden);
+
 protected:
     bool eventFilter(QObject *obj, QEvent *ev) override;
     bool event(QEvent *ev) override;