Toggled spoilers on click

Resolves #988.

http://jenkins.buttonweavers.com:8080/job/buttonmen-AdmiralJota/243/

Dependent on #1105.
It feels slightly awkward, to have two classes which you toggle between in this way, and which just have to be manually kept one-on/one-off to satisfy an invariant.  Would it make sense to have a class, "chatSpoiler", which was always on for a spoiler, and a single second class "showSpoiler" or something, which was the only thing that got toggled?

This is just a cleanliness thought, and it's minor.