CHG: Migrated courses are no more hidden but keep the same visibility state as...

CHG: Migrated courses are no more hidden but keep the same visibility state as the remote course one.
BUG: Correcting delete_backup CLI command ignoring fileid argument.
BUG: Correcting error filter criteria on requests management page.
ENH: Adding migrated course URL in notification email to requester on successful migration.
ENH: Adding checks on webservices calls to reschedule notification tasks to server if errors in callbacks (remote server on maintenance mode, etc.).
ENH: Preventing multiple course backup for the same request on reschedulded local backup task (due to requester server not acknowledging end of backup).