Type: feature

The following has been addressed in the PR:

• There is a related issue
• All code matches the style guide
• Unit or Functional tests are included in the PR

Description:
If I'm understanding the code correctly, the widget won't render until it's attached to the projector. That happens here, in the callback that gets called when the custom element is attached to the DOM. So until that point we don't need to worry about a MutationObserver, because we can just capture the state of the element when it's attached and set the appropriate children at that time. This has the added benefit of letting things like replaceChild and insertBefore work as expected, without a lot of additional logic.

If we want to be able to add children after the element is attached then we will probably need to track the elements we've seen and use a MutationObserver to detect new children and create widgets for them. That should probably be a separate PR though.

Resolves #531