BTTV Pro Badges are always 3x (72px)

[Nerixyz]

I'm adding support for BTTV Pro badges in Chatterino here: Chatterino/chatterino2#6625. I noticed that the badges only provide a 72px version. BTTV emotes provide three sizes. It would be great if badges could do the same. Specifically, if there were the following sizes:

• 1x at 18px
• 2x at 36px
• 3x at 72px (current)

To remain backwards compatible, the badge in the user_update event could get an additional id field that clients can use with a template (similar to emotes). For example https://cdn.betterttv.net/badge/{id}/{size}.webp.