refactor: rename the atom directory to shell

shell/app/manifests.h

@@ -0,0 +1,16 @@
+// Copyright (c) 2019 GitHub, Inc.
+// Use of this source code is governed by the MIT license that can be
+// found in the LICENSE file.
+
+#ifndef ATOM_APP_MANIFESTS_H_
+#define ATOM_APP_MANIFESTS_H_
+
+#include <vector>
+
+#include "services/service_manager/public/cpp/manifest.h"
+
+const service_manager::Manifest& GetElectronContentBrowserOverlayManifest();
+const std::vector<service_manager::Manifest>&
+GetElectronBuiltinServiceManifests();
+
+#endif  // ATOM_APP_MANIFESTS_H_