Reactions - display users on hover

You should be able to see who has reacted to comments by hovering on the reactions.

Hover message should be:

usernameA, usernameB, usernameC reacted with thumbs up

NB. We don’t cap the number of usernames (can do this later if necessary).

Steps

1. Backend: Render HTML reaction meta elements (1 for each reaction, no hover behaviour)
2. Frontend: Add hover behaviour