Figure out some kind of autohiding mechanism for multi-row tabs

[sonofevil]

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These two stylesheets don't work well together. In particular, the height of the "hidden" tabs toolbar is still governed by the height of the multiple tab row, so just a big empty space if you have several rows. There is also the problem that if you right-click a tab, the tab bar gets hidden. But I assume this is because the context menu blocks the hover property, and I'm not sure if that's fixable.

I tried writing my own fixes, but I don't understand the logic of autohide_tabstoolbar.css and my results are very clunky. Would love a compatibility patch that makes them play together in an intuitive way.