Use callbacks to apply calendar settings changes

Every changed setting in a GcalEditCalendarPage of the GcalCalendarManagementDialog is applied only when clicking the back button.

This means that users:

• can't see changes until pressing the back button (events in the background main window do not change color instantaneously);
• will lose unapplied changes when the dialog becomes a bottom sheet and the bottom sheet is closed by swiping down or clicking above it;
• can't easily close the dialog, because the close button was removed to try to mitigate unapplied changes loss.

The issue of the missing close button was first raised in #1191.

A fix was proposed in !466, but it didn't take into account that unapplied changes are lost when closing the dialog.

This MR makes all settings be applied when they are changed, instead of waiting for the back button or the escape key to be pressed.

before	after
Capture_vidéo_du_2024-11-09_17-09-47	Capture_vidéo_du_2024-11-09_17-10-45