macOS: disable AppNap during sync

Signed-off-by: Alexey Ivanov <alexey.ivanes@gmail.com>

src/qt/macos_appnap.h

@@ -0,0 +1,24 @@
+// Copyright (c) 2011-2018 The Bitcoin Core developers
+// Distributed under the MIT software license, see the accompanying
+// file COPYING or http://www.opensource.org/licenses/mit-license.php.
+
+#ifndef BITCOIN_QT_MACOS_APPNAP_H
+#define BITCOIN_QT_MACOS_APPNAP_H
+
+#include <memory>
+
+class CAppNapInhibitor final
+{
+public:
+    explicit CAppNapInhibitor();
+    ~CAppNapInhibitor();
+
+    void disableAppNap();
+    void enableAppNap();
+
+private:
+    class CAppNapImpl;
+    std::unique_ptr<CAppNapImpl> impl;
+};
+
+#endif // BITCOIN_QT_MACOS_APPNAP_H