cleanup in item::* namespace
most functions were already moved into the content::item namespace,
but a few were left.
- marked the following function as deprecated
* item::get_content
* item::content_is_null
* item::get_revision_content
* item::content_methods_by_type
* item::publish
* item::unpublish
- added new functions:
* content::item::content_is_null
* content::item::content_methods_by_type
* content::item::get_content
* content::item::get_revision_content
* content::item::publish
* content::item::unpublish
- updated regression test
