Discuss visibilityjs

Looking at our uses of visibilityjs, I'm not sure what problem the lib is solving.

The main use case for this library is to enable some of the times* only when content is visible to the user

* typo from the docs, they meant "timers"

We're not even using all of the stuff they've regarded "low-level". So I'm not sure how this is any better than the vanilla API.

Should we remove it?