panel-switcher: Allow going back to same page in folded mode
Call adw_navigation_split_view_set_show_content() in on_row_activated() to ensure that AdwNavigationSplitView always shows the content page when clicking the row in folded mode. When the stack page does not change (when going back from a page and selecting the same page again), this does not work otherwise.
For this we need a reference to the parent AdwNavigationSplitView in MsPanelSwitcher. Add it as a 'parent-split-view' property, and set it in the main window ui-file.
Fixes #38 (closed).