Remove notification group before child notifications

Otherwise, removing the notifications can cause an extra tone/banner to
trigger when the group is implicitly updated.
Remove persistent notifications file

We can read all of this from properties of the actual notifications
stored by the system instead.
WIP Port directly over to nemonotifications
WIP Restore from notifications db
WIP Fixup port PersonalNotification to nemo
Fixup sync
WIP Restore notifications on startup
WIP Fine tune notification usage