[Forms] Add CompositeController

Add a controller for composite controls; this is used
to flag contained controls as required when they have
been partially filled in (to treat entering one of two
such fields as invalid.) WTD-593.

platform/forms/src/controllers/CompositeController.js

@@ -0,0 +1,27 @@
+/*global define*/
+
+define(
+    [],
+    function () {
+        "use strict";
+
+        function CompositeController() {
+            function isDefined(element) {
+                return typeof element !== 'undefined';
+            }
+
+            function or(a, b) {
+                return a || b;
+            }
+
+            return {
+                isNonEmpty: function (value) {
+                    return (value || []).map(isDefined).reduce(or, false);
+                }
+            };
+        }
+
+        return CompositeController;
+
+    }
+);