GradingPeriod
$id : integer
$startDate : \DateTime
$endDate : \DateTime
$schoolYear : integer
$updatedDate : \Pivot\Client\Entities\datetime
__construct()
getId()
setStartDate( $date)
getStartDate()
setEndDate( $date)
getEndDate()
setSchoolYear( $year)
getSchoolYear()
setUpdatedDate(\DateTime $date)
getUpdatedDate()