Add missing parent for messagebox and other popups

Unparented popups can easily get lost in backround, but they still block top level event loop when run with ::exec() thus preventing interactions with main window.  This mainly happens on wayland. Setting the parent ensures they are always kept on top and reasonably positioned.

src/Mod/TechDraw/Gui/Command.cpp

@@ -424,7 +424,7 @@ void CmdTechDrawView::activated(int iMsg)
             bool dontShowAgain = hGrp->GetBool("DontShowInsertFileMessage", false);
             if (!dontShowAgain) {
                 auto msgText = QObject::tr("If you want to insert a view from existing objects, please select them before invoking this tool. Without a selection, a file browser will open, to insert a SVG or image file.");
-                QMessageBox msgBox;
+                QMessageBox msgBox(Gui::getMainWindow());
                 msgBox.setText(msgText);
                 auto dontShowMsg = QObject::tr("Do not show this message again");
                 QCheckBox dontShowCheckBox(dontShowMsg, &msgBox);