Work/rrosch/show places icons

It seems that not setting the icon size actually caused the icons in the Places sidebar tree to not display at all. It looks good for me at 16x16, but optimally it should pick up whatever size the user has selected other widgets to be. For now, at least this shows the icons again.

I think I did the merge request wrong, since it contains the commit from !42 (merged) which hasn't been merged yet. Let me know if I need to fix that here or if it's ok as-is.