fixed names of acs_objects to be specific to acs-mail (as opposed to acs-messaging)
changed object_id to gc_object_id in __create_type so that drop_type works!
changed content_object_id (fk acs_content) to content_item_id (referring to CR)
added 'on delete cascade' to acs_mail_links
added command to source acs_mail_nt_create.sql