Prevent cursor_pred flicker properly

cursor_pred could have been visibility: hidden for a while if:
 - a prediction is shown (display:none -> shown)
 - the server rejects a prediction (resetGUI -> visibility hidden)
Update prune predictions cronjob

 - avoid using bash expansions for speed
 - ls -l reports one more prediction than there actually is
 - modify crontab for    crontab -u www-data crontab-example