[Containment] Implement Link

Implement link as a basic action, to separate it out from
drop gesture such that it can be controlled by policy. For
WTD-962.

platform/commonUI/edit/src/actions/LinkAction.js

@@ -0,0 +1,47 @@
+/*global define*/
+
+define(
+    [],
+    function () {
+        "use strict";
+
+
+        /**
+         * Add one domain object to another's composition.
+         */
+        function LinkAction(context) {
+            var domainObject = (context || {}).domainObject,
+                selectedObject = (context || {}).selectedObject,
+                selectedId = selectedObject && selectedObject.getId();
+
+            // Add this domain object's identifier
+            function addId(model) {
+                model.composition = model.composition || [];
+                model.composition.push(selectedId);
+            }
+
+            // Persist changes to the domain object
+            function doPersist() {
+                var persistence = domainObject.getCapability('persistence');
+                return persistence.persist();
+            }
+
+            // Link these objects
+            function doLink() {
+                return domainObject.useCapability("mutation", addId)
+                    .then(doPersist);
+            }
+
+            return {
+                /**
+                 * Perform this action.
+                 */
+                perform: function () {
+                    return selectedId && doLink();
+                }
+            };
+        }
+
+        return LinkAction;
+    }
+);