Start working on a Downloader app and backing classes in LibGUI.

LibGUI is slowly becoming LibKitchensink but I'm okay with this for now.

LibGUI/GHttpNetworkJob.h

@@ -0,0 +1,20 @@
+#pragma once
+
+#include <LibGUI/GNetworkJob.h>
+#include <LibGUI/GHttpRequest.h>
+
+class GTCPSocket;
+
+class GHttpNetworkJob final : public GNetworkJob {
+public:
+    explicit GHttpNetworkJob(const GHttpRequest&);
+    virtual ~GHttpNetworkJob() override;
+
+    virtual void start() override;
+
+    virtual const char* class_name() const override { return "GHttpNetworkJob"; }
+
+private:
+    GHttpRequest m_request;
+    GTCPSocket* m_socket { nullptr };
+};