Make KFileItemActions the parent of the actions it creates

This prevents the problem that the destructor of KFileItemActions may
delete dangling pointers if the widget that is set with setParentWidget
is destroyed before the KFileItemActions instance (note that this widget
was the parent of the actions before this commit, but that
KFileItemActions stll remembered them in d->m_ownActions and deleted
them in the destructor.)

REVIEW: 114921