Strike-through code button & spoiler button

[Braixen]

I think a spoiler button would be useful because a spoiler has many applications and we encourage it's use for large images and spoiling content in a sense. In terms of the strikethrough I don't think it's applicable enough for its own button (unless it's incredibly easy to implement and is really "no harm done"). I find it's useful to have a BBcode resource on sites/forums and we could set that up to inform of the [s ][/s] code. In terms of a suggestion tag that seems it would be helpful/useful from my perspective.