Improve timingView with display of the ASS lines

Display the Ass lines on the timingView.

Allow for Drag & Drop of bars to change syl duration / line start and end time of the AssLineModels only (as changes are not written back to the Ass file yet).

src/UI/DocumentViews/AudioVisualizer/TimingAxis.hh

+#ifndef VIVY_TIMING_AXIS_H
+#define VIVY_TIMING_AXIS_H
+
+#ifndef __cplusplus
+#error "This is a C++ header"
+#endif
+
+#include "PreCompiledHeaders.hh"
+#include <cmath>
+
+namespace Vivy
+{
+class TimingAxis final : public QGraphicsObject {
+    Q_OBJECT
+
+public:
+    explicit TimingAxis() noexcept;
+    ~TimingAxis() noexcept override = default;
+
+    QRectF boundingRect() const override;
+    void paint(QPainter *painter, const QStyleOptionGraphicsItem *option, QWidget *widget) override;
+
+private:
+    static inline constexpr QColor axisColour = QColor(255, 220, 220);
+    QPen pen;
+    int penWidth{ 1 };
+
+    /*
+     * We use ints here because
+     * qPainter->drawLine() and qPainter->drawText()
+     * restrict us to ints anyways
+     */
+    QVector<int> availableTicks = { 10, 100, 1000, 10000, 60000, 3600000, 86400000 };
+    int minBetweenMinor{ 10 };
+    int minorTicks;
+    int majorTicks;
+
+    int minorTicksHeight{ 3 };
+    int majorTicksHeight{ 7 };
+    int timeDigitsHeight{ 20 };
+    int timeDigitsMargin{ 3 };
+
+protected:
+public slots:
+    void refreshTicks();
+};
+
+}
+
+#endif // VIVY_TIMING_AXIS_H