Added progressiveId for multi-parcel shipments

[damianostevanato]

From gls documentation , when creating a multi-parcel shipments its required to specify an auto-increment id, i've added a setter and getter method to add this property so i can use this package to create multi-parcel shipments so now it can be setted like this

$parcel->setProgressiveId(random_int(100000000,999999999));

and this should be set for every parcel created

[damianostevanato]

im closing this pull request because i need to do major updates