When the user deletes a calendar in the calendar management dialog, a
popover allows them to undo the deletion. The calendar is fully deleted
only when the toast is dismissed or when the toast reaches its timeout.
When the user closes the calendar management dialog without dismissing
the toast and before the end of the timeout, the calendar can still be
manipulated for a short period of time.
To fix this, I removed the calendar-management-dialog from the UI of the
window, and made the window create and destroy the dialog on demand.
This forces the toast overlay to dismiss all toasts.
The interfacing that GcalCalendarManagementDialog had is somewhat
similar to AdwNavigationView, with pages and signaling basically
matching the same semantics.
We can save some code by switching to AdwNavigationView then, as
the heavy-lifting of page management is done there now.
The headerbar of the dialog is no more; instead, each page has its
own headerbar that automatically gets a back button.
Page activation and deactivation works essentially the same, but
uses AdwNavigationView signals to manage that.
Enzo MAROS