Add offline mode support

launcher/minecraft/auth/steps/OfflineStep.h

@@ -0,0 +1,20 @@
+
+#pragma once
+#include <QObject>
+
+#include "QObjectPtr.h"
+#include "minecraft/auth/AuthStep.h"
+
+#include <katabasis/DeviceFlow.h>
+
+class OfflineStep : public AuthStep {
+    Q_OBJECT
+public:
+    explicit OfflineStep(AccountData *data);
+    virtual ~OfflineStep() noexcept;
+
+    void perform() override;
+    void rehydrate() override;
+
+    QString describe() override;
+};