all: refactor windows code out of core

There are still some links from core to window but its now separate
enough to fix PanelWindow in qml tooling.

src/window/test/popupwindow.hpp

@@ -0,0 +1,18 @@
+#pragma once
+
+#include <qobject.h>
+#include <qtmetamacros.h>
+
+class TestPopupWindow: public QObject {
+	Q_OBJECT;
+
+private slots:
+	void initiallyVisible();
+	void reloadReparent();
+	void reloadUnparent();
+	void invisibleWithoutParent();
+	void moveWithParent();
+	void attachParentLate();
+	void reparentLate();
+	void xMigrationFix();
+};