Edit history for messages

I can only support this. It creates transparency while still allowing for a smooth reading experience. Both Facebook (I know, I know) and Discourse support this feature. Not supporting it allows for some nasty surprises, where Mallory writes a message, Bob replies, and Mallory changes their message to make Bobs reply look bad. One addition could be to allow edits with the first 5 minutes (time frame subject to discussion) where the edit is only visible to instance staff, community owners and/or moderators.