Port to CMake from qmake, and split decoder into subdirectory

Qt 5 has had to be dropped as CMakeLists.txt uses qt_* specific commands
which are implemented in Qt 6 onwards.

cmake --install is only working on Linux at the moment; it installs the
executable and the bundled example tti files into /usr/local/share/doc

The teletext decoder with its document storage has been moved to a
subdirectory with the intention of making it possible to use in other
projects, but some further separation of editing stuff will be needed.

src/qteletextmaker/palettedockwidget.h

@@ -0,0 +1,59 @@
+/*
+ * Copyright (C) 2020-2024 Gavin MacGregor
+ *
+ * This file is part of QTeletextMaker.
+ *
+ * QTeletextMaker is free software: you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License as published by
+ * the Free Software Foundation, either version 3 of the License, or
+ * (at your option) any later version.
+ *
+ * QTeletextMaker is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with QTeletextMaker.  If not, see <https://www.gnu.org/licenses/>.
+ */
+
+#ifndef PALETTEDOCKWIDGET_H
+#define PALETTEDOCKWIDGET_H
+
+#include <QCheckBox>
+#include <QDockWidget>
+#include <QPushButton>
+
+#include "mainwidget.h"
+
+class PaletteDockWidget : public QDockWidget
+{
+	Q_OBJECT
+
+public:
+	PaletteDockWidget(TeletextWidget *parent);
+	void updateAllColourButtons();
+
+public slots:
+	void updateColourButton(int colourIndex);
+	void setLevel3p5Accepted(bool b);
+
+protected:
+	void showEvent(QShowEvent *event);
+
+private slots:
+	void selectColour(int colourIndex);
+	void setLevel3p5Seen(bool b);
+	void updateLevel3p5Cursor();
+
+private:
+	void resetCLUT(int colourTable);
+
+	QPushButton *m_colourButton[32], *m_resetButton[4];
+	QCheckBox *m_showHexValuesCheckBox;
+	bool m_level3p5Accepted, m_level3p5Seen;
+
+	TeletextWidget *m_parentMainWidget;
+};
+
+#endif