[calamares] Decouple debug-window button

- Provide slots and signals for managing the debug-window,
  so it can be used from QML as well.

src/calamares/CalamaresWindow.cpp

@@ -103,24 +103,8 @@ CalamaresWindow::getWidgetSidebar( QWidget* parent, int desiredWidth )
         sideLayout->addWidget( debugWindowBtn );
         debugWindowBtn->setFlat( true );
         debugWindowBtn->setCheckable( true );
-        connect( debugWindowBtn, &QPushButton::clicked, this, [=]( bool checked ) {
-            if ( checked )
-            {
-                m_debugWindow = new Calamares::DebugWindow();
-                m_debugWindow->show();
-                connect( m_debugWindow.data(), &Calamares::DebugWindow::closed, this, [=]() {
-                    m_debugWindow->deleteLater();
-                    debugWindowBtn->setChecked( false );
-                } );
-            }
-            else
-            {
-                if ( m_debugWindow )
-                {
-                    m_debugWindow->deleteLater();
-                }
-            }
-        } );
+        connect( debugWindowBtn, &QPushButton::clicked, this, &CalamaresWindow::showDebugWindow );
+        connect( this, &CalamaresWindow::debugWindowShown, debugWindowBtn, &QPushButton::setChecked );
     }
 
     CalamaresUtils::unmarginLayout( sideLayout );
@@ -430,6 +414,29 @@ CalamaresWindow::ensureSize( QSize size )
     resize( w, h );
 }
 
+void
+CalamaresWindow::showDebugWindow( bool show )
+{
+    if ( show )
+    {
+        m_debugWindow = new Calamares::DebugWindow();
+        m_debugWindow->show();
+        connect( m_debugWindow.data(), &Calamares::DebugWindow::closed, this, [=]() {
+            m_debugWindow->deleteLater();
+            emit debugWindowShown( false );
+        } );
+        emit debugWindowShown( true );
+    }
+    else
+    {
+        if ( m_debugWindow )
+        {
+            m_debugWindow->deleteLater();
+        }
+        emit debugWindowShown( false );
+    }
+}
+
 void
 CalamaresWindow::closeEvent( QCloseEvent* event )
 {

src/calamares/CalamaresWindow.h

@@ -30,7 +30,7 @@ public:
     CalamaresWindow( QWidget* parent = nullptr );
     ~CalamaresWindow() override {}
 
-public slots:
+public Q_SLOTS:
     /**
      * This asks the main window to grow to accomodate @p size pixels, to accomodate
      * larger-than-expected window contents. The enlargement may be silently
@@ -38,6 +38,17 @@ public slots:
      */
     void ensureSize( QSize size );
 
+    /** @brief Set visibility of debug window
+     *
+     * Shows or hides the debug window, depending on @p show.
+     * If Calamares is not in debug mode, nothing happens and the debug
+     * window remains hidden.
+     */
+    void showDebugWindow( bool show );
+
+Q_SIGNALS:
+    void debugWindowShown( bool show );
+
 protected:
     virtual void closeEvent( QCloseEvent* e ) override;