Add Qt Marketplace plugin

Provides a simple integration into the welcome page.

Task-number: QTCREATORBUG-23452
Change-Id: I3e615dcd6dfd9e401159ea6d30b48737edb1e1f9
Reviewed-by: David Schulz <david.schulz@qt.io>
Reviewed-by: Christian Stenger <christian.stenger@qt.io>

src/plugins/marketplace/marketplaceplugin.h

@@ -0,0 +1,49 @@
+/****************************************************************************
+**
+** Copyright (C) 2019 The Qt Company Ltd.
+** Contact: https://www.qt.io/licensing/
+**
+** This file is part of Qt Creator.
+**
+** Commercial License Usage
+** Licensees holding valid commercial Qt licenses may use this file in
+** accordance with the commercial license agreement provided with the
+** Software or, alternatively, in accordance with the terms contained in
+** a written agreement between you and The Qt Company. For licensing terms
+** and conditions see https://www.qt.io/terms-conditions. For further
+** information use the contact form at https://www.qt.io/contact-us.
+**
+** GNU General Public License Usage
+** Alternatively, this file may be used under the terms of the GNU
+** General Public License version 3 as published by the Free Software
+** Foundation with exceptions as appearing in the file LICENSE.GPL3-EXCEPT
+** included in the packaging of this file. Please review the following
+** information to ensure the GNU General Public License requirements will
+** be met: https://www.gnu.org/licenses/gpl-3.0.html.
+**
+****************************************************************************/
+
+#pragma once
+
+#include <extensionsystem/iplugin.h>
+
+#include "qtmarketplacewelcomepage.h"
+
+namespace Marketplace {
+
+class MarketplacePlugin : public ExtensionSystem::IPlugin
+{
+    Q_OBJECT
+    Q_PLUGIN_METADATA(IID "org.qt-project.Qt.QtCreatorPlugin" FILE "Marketplace.json")
+
+public:
+    MarketplacePlugin() = default;
+
+    bool initialize(const QStringList &, QString *) final { return true; }
+    void extensionsInitialized() final {}
+
+private:
+    Internal::QtMarketplaceWelcomePage welcomePage;
+};
+
+} // namespace Marketplace