Review what should and shouldn't cause a post to be marked as "read"

[colejd]

I'm of the opinion that we shouldn't mark any posts as "read" unless you actually click into them. Maybe opening the media view as well. But upvoting/downvoting shouldn't do it IMO. We should look into the cases where we do this and reevaluate.

[ccrama]

Had some feedback about the peek previews, I'll add this to v6