enable storage extension (#886)

* enable storage extension

* fix -beta

libs/storage/pxt.json

@@ -1,6 +1,6 @@
 {
     "name": "storage",
-    "description": "USB Pen-drive support and flash storage",
+    "description": "USB Pen-drive support and flash storage - beta",
     "files": [
         "storage.cpp",
         "storage-core.ts",

pxtarget.json

@@ -16,7 +16,8 @@
         "libs/infrared-sensor",
         "libs/gyro-sensor",
         "libs/screen",
-        "libs/ev3"
+        "libs/ev3",
+        "libs/storage"
     ],
     "simulator": {
         "autoRun": true,