build system updates and other fixes

add preset config
import qt
separate core and frontend

src/frontend/main.h

@@ -0,0 +1,23 @@
+// Copyright 2019 threeSD Project
+// Licensed under GPLv2 or any later version
+// Refer to the license.txt file included.
+
+#pragma once
+
+#include <memory>
+#include <QDialog>
+
+namespace Ui {
+class MainDialog;
+}
+
+class MainDialog : public QDialog {
+    Q_OBJECT;
+
+public:
+    explicit MainDialog(QWidget* parent = nullptr);
+    ~MainDialog() override;
+
+private:
+    std::unique_ptr<Ui::MainDialog> ui;
+};