fix bug 1615: taskreminders not always set

on change of task reminder global setting in sysadmin, no taskreminder is set if a task is edited but dates not changed.
Most likely, task reminders are also not reset if changed by dependency tracking, because I only found this in do_task_aed.php.

put addReminder into hook_postStore to accomplish that. See mantis id 1615
wrong indentation