Add a default size for Kleopatras Main Window

This should remove the horizontal scrollbar that was otherwise
default on usual desktops. The size is realative to the screen
to avoid filling up too much space on small screens.

src/mainwindow.cpp

@@ -79,6 +79,7 @@
 #include <QProcess>
 #include <QVBoxLayout>
 #include <QMimeData>
+#include <QDesktopWidget>
 
 #include <Libkleo/KeyListModel>
 #include <Libkleo/KeyListSortFilterProxyModel>
@@ -334,6 +335,8 @@ MainWindow::Private::~Private() {}
 MainWindow::MainWindow(QWidget *parent, Qt::WindowFlags flags)
     : KXmlGuiWindow(parent, flags), d(new Private(this))
 {
+    const auto desk = QApplication::desktop()->screenGeometry(this);
+    resize(desk.width() / 2, desk.height() / 3);
 }
 
 MainWindow::~MainWindow() {}