LibCore: Move HTTP classes from LibGUI to LibCore.

LibCore/CNetworkResponse.h

@@ -0,0 +1,18 @@
+#pragma once
+
+#include <AK/Retainable.h>
+#include <AK/ByteBuffer.h>
+
+class CNetworkResponse : public Retainable<CNetworkResponse> {
+public:
+    virtual ~CNetworkResponse();
+
+    bool is_error() const { return m_error; }
+    const ByteBuffer& payload() const { return m_payload; }
+
+protected:
+    explicit CNetworkResponse(ByteBuffer&&);
+
+    bool m_error { false };
+    ByteBuffer m_payload;
+};