[Build] Declare screenfull

...and shim such that it can be acquired in the normal AMD way.
Avoids use of global variable to satisfy JSHint.

platform/commonUI/browse/src/windowing/FullscreenAction.js

@@ -25,7 +25,7 @@
  */
 define(
     ["screenfull"],
-    function () {
+    function (screenfull) {
 
         var ENTER_FULLSCREEN = "Enter full screen mode",
             EXIT_FULLSCREEN = "Exit full screen mode";