[Fixed Position] Add image proxy

Add selection proxy for image elements to support image URL
dialog, WTD-881.

platform/features/layout/src/elements/ImageProxy.js

@@ -0,0 +1,35 @@
+/*global define*/
+
+define(
+    ['./ElementProxy', './AccessorMutator'],
+    function (ElementProxy, AccessorMutator) {
+        'use strict';
+
+        /**
+         * Selection proxy for Image elements in a fixed position view.
+         *
+         * Note that arguments here are meant to match those expected
+         * by `Array.prototype.map`
+         *
+         * @constructor
+         * @param element the fixed position element, as stored in its
+         *        configuration
+         * @param index the element's index within its array
+         * @param {Array} elements the full array of elements
+         */
+        function ImageProxy(element, index, elements) {
+            var proxy = new ElementProxy(element, index, elements);
+
+            /**
+             * Get and/or set the displayed text of this element.
+             * @param {string} [text] the new text (if setting)
+             * @returns {string} the text
+             */
+            proxy.url = new AccessorMutator(element, 'url');
+
+            return proxy;
+        }
+
+        return ImageProxy;
+    }
+);

platform/features/layout/src/elements/TextProxy.js

@@ -27,6 +27,13 @@ define(
              */
             proxy.color = new AccessorMutator(element, 'color');
 
+            /**
+             * Get and/or set the displayed text of this element.
+             * @param {string} [text] the new text (if setting)
+             * @returns {string} the text
+             */
+            proxy.text = new AccessorMutator(element, 'text');
+
             return proxy;
         }