Deprecate/rewrite fedora_item.

Developers should prefer to use the interface provided by Tuque.
Fedora_Item has been rewritten to use Tuque where possible to ease
migration to the new API.

Also, includes a backport of the Tuque wrapper from 7.x, to make a large
number of hooks available (haven't yet ported the api.php back that
describes the available hooks...).