Add image lazy loading to Five for the Future pages

[jonoaldersonwp]

Templates like ​https://wordpress.org/five-for-the-future/pledges/ and ​https://wordpress.org/five-for-the-future/pledge/yoast/ load a *lot* of images. This causes a number of performance issues, which results in a page which loads slowly / feels slow.

Much of this could be mitigated by adding a loading=lazy attribute to avatar images.

[dd32]

5ftf issues can be submitted directly to the source repo for that site: ​https://github.com/wordpress/five-for-the-future

This will need to be migrated upstream at some point.

[dd32]

Nevermind, here it is: ​https://github.com/WordPress/five-for-the-future/issues/131