Add support for JavaScript API

Updated patch (added $email identify value based on user->mail)

Updated description

Ah, maybe I'm just too new to Klaviyo in order to get this..

We're going to use Klaviyo to store user behavior (among other things) for our e-commerce store. I was under the impression that the javascript API would be able to help with that, especially for users that are not logged in. I've been told that the javascript implementation can find the possible identity of a user by pairing mac-addresses, IP-addresses etc, thus being able to store user data when a user is not logged in - simply by the fact that Klaviyo still knows who the user is assigning a cookie. Since the site is cached for anonymous users, we'd have to rely on javascript to process and send that information to Klaviyo.

The features that this module currently provides (user entity sync + API wrapper?) is not really something that the javascript frontend API should ever handle imho.

Or am I missing something here? :)

Update: I've implemented my patch live on a production site to try it out, and I've also tried to read up a bit more on the Klaviyo API. It seems to work well. The javascript snippet adds automatic tracking of visited pages for example, on the "Active on site" metric.

I'm still not sure how it works for non-identified users, but the documentation only mentions this:

You need to make one change to the snippet. If you're an eCommerce business, remove the four lines with the "identify" call. If you're a website or web app people log into, replace the logged.in.user@example.com placeholder email with the appropriate template variable that has the logged in user's email address.

Anyway, it seems obvious to me that the javascript API adds another set of functionality.

1. Pull all JS into an individual JS file
2. Use the #attached and add the new JS file and settings the render array.

1. I was initially planning to do that, but realized that I would need to add the user's e-mail address to Drupal.settings or similar in order to make it available to the snippet, and I wasn't sure what best practice for that would be.

2. How do I use #attached for a page? I've only used it for blocks and forms.

Added description and separated the javascript snippet into a js file. Still uses drupal_add_js though.

Also added the javascript variable to the uninstall hook.

New patch supplied, using #attached. In regards to the additional features listed in #9, could we postpone those perhaps? The current patch provides basic support that should work well for most users. I wouldn't mind adding those features myself but my time is limited atm.