Allow both UI and automated backups to be created without
including files. Instead include only file references.
This is essentially implementing "SAMESITE" to backup files
instead of only for import and export functionality.
A new backup setting to include files (defaults to yes)
has been included.
The restore process will also look for and attempt to
restore files from the trashdir as part of restoring
backups. Additionally to support this process the
ammount of time files are kept in trashdir before they
are cleaned up via cron is also adjustable via admin
setting.
Changed the course libs such that module and section deletion is now
handed off to relevant functions in the util class and exempted
modules scheduled for deletion from the course backups.
