ias.getEvents() => [[event_id, event_type, actor, amount, extended_info],...]
		     event_id: unique integer
		     event_type: CHANGE_USER_CREDIT,  CHANGE_ADMIN_DEPOSIT, ADD_USER, DEL_USER
		     actor: username of admin performing the job
		     amount: integer amount of credit change
		     extended_info: dictionary of other informations. user_id=>user_id
		    						      admin_username=>admin_username

ias.delEvent([event_id, ....]):	delete event with id event_id

ias.getCreditUsage(user_id, date_from): 