gui: Add close window shortcut

CMD+W/CTRL+W is the standard shortcut to close a window without
exiting the program.

src/qt/guiutil.cpp

@@ -54,6 +54,7 @@
 #include <QSettings>
 #include <QSize>
 #include <QString>
+#include <QShortcut>
 #include <QTextDocument> // for Qt::mightBeRichText
 #include <QThread>
 #include <QUrlQuery>
@@ -378,6 +379,11 @@ void bringToFront(QWidget* w)
     }
 }
 
+void handleCloseWindowShortcut(QWidget* w)
+{
+    QObject::connect(new QShortcut(QKeySequence(Qt::CTRL + Qt::Key_W), w), &QShortcut::activated, w, &QWidget::close);
+}
+
 void openDebugLogfile()
 {
     fs::path pathDebug = GetDataDir() / "debug.log";