NOISSUE refactor *Download into more, smaller pieces

* Download is now Download.
* Download uses Sink subclasses to process various events.
* Validators can be used to further customize the Sink behaviour.

api/logic/net/MetaCacheSink.h

@@ -0,0 +1,21 @@
+#pragma once
+#include "FileSink.h"
+#include "ChecksumValidator.h"
+#include "net/HttpMetaCache.h"
+
+namespace Net {
+class MetaCacheSink : public FileSink
+{
+public: /* con/des */
+	MetaCacheSink(MetaEntryPtr entry, ChecksumValidator * md5sum);
+	virtual ~MetaCacheSink();
+
+protected: /* methods */
+	JobStatus initCache(QNetworkRequest & request) override;
+	JobStatus finalizeCache(QNetworkReply & reply) override;
+
+private: /* data */
+	MetaEntryPtr m_entry;
+	ChecksumValidator * m_md5Node;
+};
+}