Expose Chartbeat config globally

Hi there!

The Chartbeat pinger (chartbeat.js) requires the configuration (`_sf_async_config`) to be available as a global. As it stands right now, any settings being used for Chartbeat are getting ignored.

For an example, the Chartbeat pings send the `g` parameter in the URL as null. `g` represents the UID, which the JS grabs from the global config. If you look at the Chartbeat pings in your browser, they're being sent as null.

Let me know if you have any questions or I missed something. :)