How can I edit or clear the application list in the Notifications plug? Some old uninstalled apps are still in the list.
The list of apps and their notification settings is held in gsettings at
org.pantheon.desktop.gala.notifications apps. You can edit this either directly with the
gsettings command in Terminal or by installing dconf Editor.
There is currently some work being done to handle this automatically in the future. You can track the issue here: https://bugs.launchpad.net/switchboard-plug-notifications/+bug/1406799