Make toolbar rendering fast

Now that overlayslayer is in core, the toolbar loads much more frequently than before and it's initialization is slow. It makes page loading particularly ugly.

Toolbar should be loaded like the no-js version on page load (and opening the menu tray by default in the no-js version) and get initialized when the user scroll.

That way the page won't jump around when the page loads. Hopefully we can make a few things a bit simpler as well.