Render and define custom emoji/reactions

[ajkessel]

Matrix now has a spec for custom emojis that can be used in reactions. Some clients have limited support. Would be great if Nil could at least render mxc:// urls in reactions.

matrix-org/matrix-spec-proposals#4027

[mszpro]

Good idea! I think I can implement a lot to detect Matrix media URL and show them inline with the text.