rename "microbit" package to "core" #414 (#270)

* rename "microbit" package to "core" #414

* shouldn't edit the package id.

* updating package.json

* updated the wrong version

* missed updating pxt.json of tests

libs/test-snippets/pxt.json

@@ -7,7 +7,7 @@
     ],
     "public": true,
     "dependencies": {
-        "microbit": "file:../microbit",
-        "microbit-radio": "file:../microbit-radio"
+        "core": "file:../core",
+        "radio": "file:../radio"
     }
 }