Alternative RDF in core implementation draft

I've just hacked together some function skeletons showing some of my ideas for the rdf in core stuff - it's working on top of schema information that modules may return for arbitrary classes, which modules may expose too. Other modules can then alter this information and so change rdf properties / classes associated with it.

Implementation draft: http://drupalbin.com/9322
I've also attached a file containing the draft.

This should allow us to build the token patch on top of it, but also
* it does lazy loading, so there is no need load stuff that isn't need anyway
* it allows using callbacks for retrieving the actual property value
* for drupal_render one could just add #rdf_class and #rdf_property to an element, where the first is a reference on a RDFClass object as in code. So only if really used, the properties are fetched and integrated into the theme easily.
* having some schema information for the properties in place makes it easy to identify whether some other RDF Properties are compatible, so a contrib module could build an UI for selecting such properties.
* Field types can provide their schema information, so we can generate a (new) property on the fly.

We could use the xsd datatypes for the 'datatype' property of literals directly, but I think it's simpler with just using php primitive data types and then do an automatically mapping to xsd types when generating a real rdf schema.

Open questions are, how literals should be represented. If the language or a datatype is specified, we could add another (php)class for them or just an array. For simplicity we should also support using php primitive datatypes (string, integer,...).