Multiple handles for Activity Intents

@benpate@mastodon.social "You’re exactly right" triggered :scream: I think it's wise to be hesitant about it. I think a Create intent with inReplyTo does already mean "Reply", so right now I don't see any reason to introduce a new intent. I had a similar thought about unvoting, which is something NodeBB does but isn't captured by ActivityStreams. We had to map it to Undo(Vote). So I was wondering if Undo would make sense in 3b86, but the Undo Intent already exists and would be more cromulent.