This allows the window to be folded to show either the sidebar or the
panel when not enough space is available.
This reverts commit 2854669f5c8280a32d0b5fa6c5399cc391ef06f3.
This will help ensuring the shell's leaflets fold consistently for all
panels by setting a more reasonable minimum size constraint for the
right panel, so that more panels can meet it.
Ensure all panels take at least 300pt of width to ensure a minimum of
usability, readability of the panels and consistency of when the shell
folds itself.
With the new sidebar view in place, a new problem arose: we
need the current panel to be configured to update the title,
but cc_panel_list_add_sidebar_widget() changes the view while
activating the panel. That makes Settings crash.
Fix that by explicitly updating the headerbar widget, instead
of using notify::view of the panel list.
Only the date time panel used it, all other panels add their own shell using
cc_shell_embed_widget_in_header which was added after the date time panel was
written. Update the date time panel to use this method.
