Default email notification template should use a translated application name

Right now the default notification email template uses an untranslated descriptor application name when sending notifications.
However the documentation in https://extensions.xwiki.org/xwiki/bin/view/Extension/Notifications%20API/#HRecordableEventDescriptor advise to use a translation key for the application name, and that's what we do in general for custom events.
We also call the localization script service to render the application name in the notification settings macro, so it makes sense to do the same in the email notification template.