HG- 198 top bar slides when scrolling

So the stock classes that headroom uses are in the style convention of BEM classes. We don't use BEM so let's not use these class names. In the [headroom options](https://github.com/WickyNilliams/headroom.js#options), you can change the class names that headroom adds for it's various states. Lets just replace all `--`'s with a single `-`.

eg. `.headroom--pinned` becomes `.headroom-pinned`.