Feature Request: Lazy load icons in the editor

[JiveDig]

I've been playing with a helper class to load custom icons from the theme (via #29). If the theme tries to load many icons, it can add hundreds of ms to each page load.

I'm proposing that any custom icons (and possibly the default ones, too) be lazy-loaded/added when the icon block is added or edited for the first time. If the available icons are not stored using any sort of state/caching/etc., that would be helpful as well.

[eduwass]

This would be a nice improvement.

I have built this custom plugin that adds over 2,000 icons. While it's functional, you can tell that it struggles a bit, especially on lower-end devices.

Doing some kind of optimization like this would definitely be a great addition.