Missing "Promote to Group Label" button in labels page

After changing labels to use a presenter in https://gitlab.com/gitlab-org/gitlab-ee/merge_requests/10862, label.is_a?(ProjectLabel) is not working properly because label here is now a LabelPresenter.

This causes the missing "Promote to Group Label" button and the wrong tooltip in the subscribe button because of the same code in LabelsHelper.label_status_tooltip

Also, label.subject.name in the delete modal is now returning the label name instead of the parent. I think this should now be label.issuable_subject.name

cc @jprovaznik