Use accelerated hashing for verification

Modern CPUs have special instructions to accelerate computing
SHA hashes.
The Qt QCryptographicHash code is standard C, so not taking
advantage of those though.
Outsource the hashing to OpenSSL that does.

Shaves off some seconds during verification stage.

downloadextractthread.h

@@ -41,7 +41,7 @@ protected:
     std::mutex _queueMutex;
     std::condition_variable _cv;
     bool _ethreadStarted, _isImage;
-    QCryptographicHash _inputHash;
+    AcceleratedCryptographicHash _inputHash;
     int _activeBuf;
     bool _writeThreadStarted;
     QFuture<size_t> _writeFuture;