Various improvements

• Do now shrink if max_delay is less that actual_max_delay. Do not chage time if delay < 0.5 max_delay
• SNR of external events is zero.
• Add definition for SNR, and ifo of an event.
• Add log entry to the created event to report that was created using meg.
• Shown message about using parent S-event. Save files only if --loginfo is set.