Code review comment for lp:~victored/pantheon-files/hidden-source-list-expanders

Now that I think more about it, that sounds like a better idea. Specially if Daniel ever wants animations.

I'll modify Granite's expander renderer to use an special style class for the expanders in main categories, and use Granite's renderer from Files, dropping gossip-cell-renderer-expander.* along the way.

Let's leave this as a proof-of-concept.