Abstract: This is one instance of service that can be tracked from service provider's site by using checking_ID.
ID - Key field.
service_ID - Foreign key linking to service table.
user_alias_ID - Foreign key linking to user_alias table.
checking_ID - This is what the whole system is built around, identifying string that user has to know to track progress of his service from service provider's site.
name - Optional name the user can give to this service instance to help him remember what it was about.
last_state - Last state of this service instance, as extracted from service provider page by cron system.
last_state_change_time - Last time the state of service instance changed.
insert_time - Time when this service instance was added to database. Is used to deleting expired instances.
notify_by_email - Flag !=0 indicating that user be notified about changes by email. If flag is set here (not NULL) it overrides setting in user table.
notify_by_phone - Flag !=0 indicating that user be notified about changes by phone. If flag is set here (it is not by default) it overrides setting in user table.