I don't think the polyfill is sufficient for our needs. As far as I can see, the polyfill fetches a given `.html` file and extracts the `<template>` content from the (now dropped from WC spec) `<element>`, then injects it (commented out) into elements in the DOM with `is` attribute that matches element name.

I think this meets specific requirements of the Settings app, but is quite far from what we need.

- What if the `is` element is not in the DOM on page load?
- We have to go about removing `<!-- -->` hack
- We want template content in Shadow DOM, this polyfill injects content into 'Light DOM'.