VungleSDK plugin for plugin-x

Hi,

Here's the code for the [Vungle](http://vungle.com) SDK plugin for plugin-x. I'm including some minor changes in the test app as well (to be able to test Vungle).
Please note that we couldn't build the android version because (for some reason) it's not building for us either using Eclipse or from the command line (errors from the cli at the end of this message).
Our plugin needs the google play services, but we believe that we should not ship google play services with our plugin, as that might create conflicts if there's ever an official google play services plugin. The solution right now, requires the dev to manually include google play services if they want to use the advertising id to be able to track users. If that's not included, then our SDK falls back to other alternatives ([more info](https://github.com/Vungle/vungle-resources/tree/master/English/Android#version-322)).
The plugin was built using cocos2d-x 3.3 rc1.

Build error for sample app:
```sh
$ ./build_native.py
...
[armeabi] StaticLibrary  : libcocos3d.a
make: *** No rule to make target `jni/../../../../../cocos/editor-support/spine/Animation.cpp', needed by `obj/local/armeabi/objs-debug/spine_static/Animation.o'.  Stop.
make: Leaving directory `/Users/rolando/Documents/vungle/cocos2d-x/cocos2d-x-3.3rc1/plugin-x/samples/HelloPlugins/proj.android'
```