Emoji were broken due to `Pleroma.Formatter` not knowing about the
auto-shortcode emoji. This moves that logic from
`Pleroma.Web.TwitterAPI.UtilController` to `Pleroma.Formatter`.

Additionally, it's now possible to specify multiple shortcode globs, and
the default globs were changed to `["/emoji/custom/**/*.png"]`, since
that's in the .gitignore and the files there would have to be shortcode
emoji anyway.