We were updating the whole places sidebar when the trash changed.
This effectively removes all rows and create new ones for every trash
state change.
Although when using GtkTreeView it was somehow ok, with the new
implementation with GtkListBox this effectively locks the UI while the
trash operations are being performed.
When performing operations for i.e. 100 files, the UI can be locked
for more than 1 minute since gvfs-trash usually takes time.
To fix this just update the icon of the trash when the state of the
trash change instead of the whole sidebar.
https://bugzilla.gnome.org/show_bug.cgi?id=762677
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.
