Object migration (#2282)

I implementation of data migrations for display layouts and fixed position elements.

src/plugins/objectMigration/plugin.js

@@ -0,0 +1,51 @@
+/*****************************************************************************
+ * Open MCT, Copyright (c) 2014-2018, United States Government
+ * as represented by the Administrator of the National Aeronautics and Space
+ * Administration. All rights reserved.
+ *
+ * Open MCT 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 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.
+ *****************************************************************************/
+
+import migrations from './Migrations.js'
+
+export default function () {
+    function needsMigration(domainObject) {        
+        return migrations.some(m => m.check(domainObject));
+    }
+
+    function migrateObject(domainObject) {
+        return migrations.filter(m => m.check(domainObject))[0]
+            .migrate(domainObject);
+    }
+
+    return function (openmct) {
+        let wrappedFunction = openmct.objects.get;
+        openmct.objects.get = function migrate(identifier) {
+            return wrappedFunction.apply(openmct.objects, [identifier])
+                .then(function (object) {
+                    if (needsMigration(object)) {
+                        migrateObject(object)
+                            .then(newObject => {
+                                openmct.objects.mutate(newObject, 'persisted', Date.now());
+                                return newObject;
+                            });
+                    }
+                    return object;
+                });
+        }        
+    };
+ }