Show reactions on comments

I saw the bell notifying me that there was an update on a card, but didn't see any activity. There should be something that indicates a reaction to a comment.

<img width="218" alt="Screen Shot 2019-08-26 at 11 30 55 AM" src="https://user-images.githubusercontent.com/385726/63713790-3749a900-c7f5-11e9-919a-52fdd34b1cf2.png">
