Make Origami lazy loading use native lazy attribute

[benwallman]

Origami was written prior to the implementation of lazy loading of image attributes.

https://caniuse.com/loading-lazy-attr

By adding loading="lazy" to img elements, the browser automatically defers loading until the image is nearly on display.

This currently has 93% browser support, and is backwards compatible where older browsers will just download the image, ignoring the attribute.

We can continue with the current approach for old browsers with a browser check, or we can remove our custom lazy loading for images entirely: https://stackoverflow.com/questions/58043418/check-native-browser-support-for-lazy-loading-images