Haskell: More compact settings/manager setup

Use PagedSettings, move related parts Manager interface there, too.

Change-Id: I079dad8bbbea39d2424a25867b08c34ab0234ad5
Reviewed-by: Christian Stenger <christian.stenger@qt.io>
Reviewed-by: Eike Ziller <eike.ziller@qt.io>

src/plugins/haskell/haskellsettings.h

@@ -0,0 +1,20 @@
+// Copyright (c) 2017 The Qt Company Ltd.
+// SPDX-License-Identifier: LicenseRef-Qt-Commercial OR GPL-3.0-only WITH Qt-GPL-exception-1.0
+
+#pragma once
+
+#include <coreplugin/dialogs/ioptionspage.h>
+
+namespace Haskell::Internal {
+
+class HaskellSettings : public Core::PagedSettings
+{
+public:
+    HaskellSettings();
+
+    Utils::StringAspect stackPath;
+};
+
+HaskellSettings &settings();
+
+} // Haskell::Internal