Unify ProgressCallbacks to a Common::ProgressCallback

src/common/progress_callback.h

@@ -0,0 +1,14 @@
+// Copyright 2021 threeSD Project
+// Licensed under GPLv2 or any later version
+// Refer to the license.txt file included.
+
+#pragma once
+
+#include <functional>
+
+namespace Common {
+
+// (current_size, total_size)
+using ProgressCallback = std::function<void(std::size_t, std::size_t)>;
+
+} // namespace Common