Better onboarding experience for AppBuilder

[tjvantoll]

This builds on #3, but personally I find the getting starting experience for using analytics in AppBuilder apps cumbersome. Specifically I find it weird that I have to include a script after I install the plugin. I know of no other Cordova plugin that works this way and it's confusing.

The only two variables the script seems to need are a product ID and an app version number. Now that AppBuilder supports plugin variables, it seems like the product ID could just become a Cordova plugin variable, and that the plugin could retrieve the version number from the app package (my suggestion in #3).

Ideally you would just install the plugin, and add this to your code:

document.addEventListener( "deviceready", function() {
    window.plugins.analytics.Start();
});

Thanks