Object resource

This pushes AT to 0.3.0, in the process, it completes the removal of ObjectResource and makes it possible to pass an existing AT::Resource class to an RdfDatastream.

Removing the singleton_class.properties stuff was key to getting running on AT 0.3.x.

There is a test reverted to pending for discussion. AT's behavior has changed slightly with respect to how it handles property names conflicting with existing methods on Resource.  This makes it impossible to override `type` in the relevant test.  AT should handle this better (see: https://github.com/no-reply/ActiveTriples/issues/44), but we should also discuss to what degree this is a backwards compatibility issue.
> I think we definitely need to communicate with adopters about this, I wouldn't be surprised if many people have 'type' properties with dc:type.
> 
> Is it acceptable (for the moment) that this fails so silently?

We're an institution which would break if this goes in and we pull it.

It wouldn't be a problem if it informed us that we were doing something bad - instead this will start silently breaking our objects.