Adds Date Time panel to the system panel as a page. https://gitlab.gnome.org/Teams/Design/settings-mockups/-/blob/master/system/system-panel.png See #2241
Set the NTP switch insensitive in the case that timedated has a CanNTP property and that property is set to false. https://bugzilla.gnome.org/show_bug.cgi?id=695253
https://bugzilla.gnome.org/show_bug.cgi?id=658352