filter emojis in emojify-insert-emoji by custom status

[mooseyboots]

i am adding emojify support to mastodon.el, an emacs client for the social network mastodon.

different instances make their own custom emoji available to their users. i'm adding functionality to download them and add them to emojify-user-emojis.

not sure if this is possible, but it would be great if the user could filter emojify-insert-emoji by custom status (yes), so as to browse/discover their instance's particular custom emoji, rather than having to first know what their names are in order to filter them out of ~ 5000 others.