feat: Use a single progress dialog when doing multiple tasks

This puts all mod downloading tasks inside a SequentialTask, which is,
for more than one task, a multi step task. This is handled by the
ProgressDialog by showing both the global progress of tasks executed,
and the individual progress of each of them.

launcher/tasks/SequentialTask.h

@@ -9,13 +9,21 @@ class SequentialTask : public Task
 {
     Q_OBJECT
 public:
-    explicit SequentialTask(QObject *parent = 0);
-    virtual ~SequentialTask() {};
+    explicit SequentialTask(QObject *parent = nullptr, const QString& task_name = "");
+    virtual ~SequentialTask();
+
+    inline auto isMultiStep() const -> bool override { return m_queue.size() > 1; };
+    auto getStepProgress() const -> qint64 override;
+    auto getStepTotalProgress() const -> qint64 override;
+
+    inline auto getStepStatus() const -> QString override { return m_step_status; }
 
     void addTask(Task::Ptr task);
 
-protected:
-    void executeTask();
+protected slots:
+    void executeTask() override;
+public slots:
+    bool abort() override;
 
 private
 slots:
@@ -24,7 +32,19 @@ slots:
     void subTaskStatus(const QString &msg);
     void subTaskProgress(qint64 current, qint64 total);
 
+signals:
+    void stepStatus(QString status);
+
 private:
+    void setStepStatus(QString status) { m_step_status = status; };
+
+private:
+    QString m_name;
+    QString m_step_status;
+
     QQueue<Task::Ptr > m_queue;
     int m_currentIndex;
+
+    qint64 m_stepProgress = 0;
+    qint64 m_stepTotalProgress = 100;
 };