[Future Request] Compact menu bar option

[tamagoez]

Usually menu bar is render with expand.
But some users who made so many pages, menu bar become so long.
That makes hard to find page.

So, I suggest to add option what makes compact menu bar default.
We can set it at theme.config.js.

Thanks.

[krjo]

I was just going to add this. I second this request. It's very hard to navigate through the long list of docs. I would say top level directories under /pages should be collapsed by default.

[dimaMachina]

This was added in mentioned pr