This is causing FilePicker to log a bunch of debug noise due to the
missing support for tree models in SortingProxyModel and it's not
helping anyone so let's just disable it.
This needs fixing in SortingProxyModel.
We were only forwarding the value to the subviews, but not storing it
in m_model_column. This would cause MultiView::model_column() to return
the wrong value.
Thanks to Daniel Bos for spotting this! :^)
A MultiView is a combination of ItemView, TableView and ColumnsView
smashed into a single widget. You can switch between the view modes
by calling MultiView::set_view_mode().
Note that MultiView inherits from StackWidget, not AbstractView.
That's purely for practical reasons, although I'm not entirely sure
if there would be some benefit to having it inherit from AbstractView.
