[Feature Request] Implement a local icon cache

[cooperaj]

It'd be nice to have the service download icons from urls (if given as urls) rather than hotlinking off to the url itself.

It's quite convenient to browse a site or application and pull an image to use as the icon (like a favicon or logo) but if the site changes something that icon can stop working.

I think that flame should download the icon on saving of the link/application and serve that one going forward.