Add App Link support

Support for Facebooks [App Link](https://developers.facebook.com/docs/applinks) standard for deep linking into native applications. Right now only support for Android - iOS support is coming soon. I've also changed the scope for internal methods to private
This should be `f("No app link available");`. This request returns data, if you use `s()` the developer will be expecting a link for example in Web App using JavaScript SDK;

```
facebookConnectPlugin.getAppLink(function (aLink) {
    // Do something with aLink
    // ...
    // Oh no, aLink is undefined!
}, null);
```