Add offline mode support

launcher/minecraft/auth/steps/OfflineStep.cpp

@@ -0,0 +1,18 @@
+#include "OfflineStep.h"
+
+#include "Application.h"
+
+OfflineStep::OfflineStep(AccountData* data) : AuthStep(data) {};
+OfflineStep::~OfflineStep() noexcept = default;
+
+QString OfflineStep::describe() {
+    return tr("Creating offline account.");
+}
+
+void OfflineStep::rehydrate() {
+    // NOOP
+}
+
+void OfflineStep::perform() {
+    emit finished(AccountTaskState::STATE_WORKING, tr("Created offline account."));
+}