[FIXED JENKINS-15472] Added parentId property

Added a new job-configuration field for parent page ID#.
Plugin verifies that page ID exists and returns an error message if not.
Actually, it doesn't even look like you're using this import at all…?  Lines 57..61 already import 5 classes from this package.  But I can't find any class that you're adding in this patchset that is needed in this wildcard import.  If you don't need it, please remove it.  If you do need a class from this package, please add it to the section at 57..61, explicitly naming the class you need.