Soyuz email generation should be part of the LP mailnotification module

[Julian Edwards]

LP uses the mailnotification module to generate emails but Soyuz is not using this so we should consider moving the code there. Also consider using event handlers to trigger the notification.
Soyuz could benefit of this change in, at least, two areas: upload and build notifications.

[Celso Providelo (cprov)]

Let's first consolidate all code related to upload-notification in PackageUpload.notify, then we will be in better position to achieve this kind of integration with mailnotification.