[Qt] Add separate configuration window for theme

include/panda_qt/config_window.hpp

@@ -0,0 +1,29 @@
+#pragma once
+
+#include <QApplication>
+#include <QComboBox>
+#include <QDialog>
+#include <QPalette>
+#include <QWidget>
+#include <QtWidgets>
+
+class ConfigWindow : public QDialog {
+	Q_OBJECT
+
+  private:
+	enum class Theme : int {
+		System = 0,
+		Light = 1,
+		Dark = 2,
+		GreetingsCat = 3,
+	};
+
+	Theme currentTheme;
+	QComboBox* themeSelect = nullptr;
+
+	void setTheme(Theme theme);
+
+  public:
+	ConfigWindow(QWidget* parent = nullptr);
+	~ConfigWindow();
+};