Address review comments and some more cleanups

• Make dataengines work fully standalone
• Fix panel icon sizing There's still an issue with the popup size when resizing the vertical panel smaller so it collapses
• Implement keyboard navigation for the list with focus hacks... Delete key closes notifications or groups, Arrow left/right expand/collapse groups, Enter invokes default action, if any
• Fix DND times that are supposed to be hidden showing ModelContextMenu doesn't respect "visible" property
• Move "Notifications" header to ListView header so it scrolls away and leaves more room for the notifications in systray popup
• Fix finished jobs in history showing as failed when app is closed
• Don't remember apps that spawned jobs, only for notifications
• Use CriticalNotification window type (patches pending)