Automated backups with external storage fill trashdir

The current backup code copies the temporary zip file to the file pool, and depending on external storage settings will then copy to this location and then potentially delete the file pool copy.

Deleting the filepool backup copy means this is sent into trashdir, which on large sites where many backups run at once can cause a huge amount of additional disk usage before the trashdir is cleared. Additionally, the additional disk operations cause the whole backup process to take much longer than it should as there is twice the work involved.

This should be changed, so that in the case where automated course backups should only be put in an external storage location they are put there directly instead of first running past the filepool and fillingtrashdir.

Somewhat ugly patch for this incoming - there might be a better way to handle this?