add: reencode album feature

for now presets which are featured in the GUI are: mp3, aac, opus, lossless.

to-refactor: AlbumReencoder.cpp, backend code is currently longer than needed! we can shorten it. with seperating the raii handlers into a seperate class

src/gui/ReencodeDialog.h

@@ -0,0 +1,54 @@
+#pragma once
+#include <QDialog>
+#include <QList>
+#include "engine/Track.h"
+#include "engine/ReencodeJob.h"
+
+class QComboBox;
+class QLineEdit;
+class QPushButton;
+class QTableWidget;
+class QLabel;
+class QProgressBar;
+
+namespace engine { class AlbumReencoder; }
+class ReencodeDialog : public QDialog {
+    Q_OBJECT
+public:
+    explicit ReencodeDialog(const QList<engine::Track> &tracks,
+                            QWidget *parent = nullptr);
+    ~ReencodeDialog();
+
+private slots:
+    void onPresetChanged(int index);
+    void onBrowseOutput();
+    void onStartStop();
+    void onTrackStarted (int index, const QString &title);
+    void onTrackFinished(int index, bool ok, const QString &outPath,
+                         const QString &err);
+    void onAllFinished  (int succeeded, int failed);
+
+private:
+    void buildUi();
+    void populateTrackTable();
+    void setRunning(bool running);
+    void updateOverallProgress();
+
+    QList<engine::Track>         m_tracks;
+    QList<engine::EncodePreset>  m_presets;
+
+    QComboBox    *m_presetCombo   { nullptr };
+    QLabel       *m_presetDesc    { nullptr };
+    QLineEdit    *m_outputDir     { nullptr };
+    QPushButton  *m_browseBtn     { nullptr };
+    QTableWidget *m_table         { nullptr };
+    QProgressBar *m_overallBar    { nullptr };
+    QLabel       *m_statusLabel   { nullptr };
+    QPushButton  *m_startStopBtn  { nullptr };
+    QPushButton  *m_closeBtn      { nullptr };
+
+    engine::AlbumReencoder *m_reencoder { nullptr };
+
+    int m_doneCount  { 0 };
+    int m_totalCount { 0 };
+};