gtkplacesidebar: use GtkListBox
We were using GTkTreeView in a simple list. Also, as we know, GtkCellRenderers are not the best way to theme and manipulate widgets. So instead use a GtkListBox to modernize the GtkPlacesSidebar, and in the way clean up some parts of the code (like headings) which were not used anymore. Also we don't use a model anymore, since the data is simple enough to manage it in a subclass of the row itself.
Showing with 2287 additions and 2085 deletions