Web worker thread for performance boost

[kangzeroo]

🤔 Originally I wanted to use a web-worker to offload JS work from the main thread so that this widget would be non-intrusive & high performance. This can be useful because some companies may be hesitant to add an embed widget to their website if the main JS thread is busy. In theory, offloading work to a separate web-worker JS thread would give a performance boost as the main JS thread is barely touched by this widget.

However in practice 🤣 loading a web-worker from a cross-origin CDN is actually a XSS security vulnerability as explained by the W3C team here in w3c/ServiceWorker#940 (comment)

There are 2 possible workarounds, but they add extra complexity and might not be worth enough juice for the squeeze:

1. Load the widget as an iframe and load the webworker in the same iframe so that its the same origin (from CDN)
2. Keep the widget NOT an iframe and instead load the webworker as base64 and convert into a script

[kangzeroo]

I intend to close this pull request and keep things simple for now, just keep the entire script in the same thread.