[Layout] Disallow folders

Disallow layouts in folders, WTD-1373.

platform/features/layout/src/LayoutCompositionPolicy.js

@@ -0,0 +1,52 @@
+/*****************************************************************************
+ * Open MCT Web, Copyright (c) 2014-2015, United States Government
+ * as represented by the Administrator of the National Aeronautics and Space
+ * Administration. All rights reserved.
+ *
+ * Open MCT Web is licensed under the Apache License, Version 2.0 (the
+ * "License"); you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ * http://www.apache.org/licenses/LICENSE-2.0.
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS, WITHOUT
+ * WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. See the
+ * License for the specific language governing permissions and limitations
+ * under the License.
+ *
+ * Open MCT Web includes source code licensed under additional open source
+ * licenses. See the Open Source Licenses file (LICENSES.md) included with
+ * this source code distribution or the Licensing information page available
+ * at runtime from the About dialog for additional information.
+ *****************************************************************************/
+/*global define*/
+
+define(
+    [],
+    function () {
+        "use strict";
+
+        /**
+         * Defines composition policy for Display Layout objects.
+         * They cannot contain folders.
+         */
+        function LayoutCompositionPolicy() {
+            return {
+                /**
+                 * Is the type identified by the candidate allowed to
+                 * contain the type described by the context?
+                 */
+                allow: function (candidate, context) {
+                    var isFolderInLayout =
+                            candidate &&
+                            context &&
+                            candidate.instanceOf('layout') &&
+                            context.instanceOf('folder');
+                    return !isFolderInLayout;
+                }
+            };
+        }
+
+        return LayoutCompositionPolicy;
+    }
+);