Duplicate to another course: Connections between activities get lost

[PhMemmel]

Currently, block_massaction is backing up and restoring the selected course modules one after another as a single activity backup and restore process. This raises an issue as soon as there are dependencies between the course modules (e. g. activities linked by mod_learningmap, access restrictions depending on completion of another activity etc.). It would be great if these dependencies could be preserved.

Most likely this could be realized by changing the way the activities are backed up and restored: Instead of backup-restore first one, then backup-restore second one etc. all activities should be backed up at once. Unfortuantely, I'm not very experienced with the backup API and I could not find low level documentation about it. So I welcome any examples/hints or - even better - pull requests :-)