Add Brick DefinedNamespace

[gtfierro]

An answer to the call in #1415

Proposed Changes

• Adds Brick classes, properties and EntityProperties into an RDFlib DefinedNamespace
• a generation script will be committed to the Brick repository to facilitate updates to RDFlib when Brick releases are done (every ~6 months for bigger releases)

Let me know if the namespace is too large: I can impose some principles for reducing the number of individuals in the file, such as only including the first 2 levels of the Brick class hierachy

[nicholascar]

Thanks @gtfierro! I don't think it's too big - ~1,000 lines of Python is nothing really, compared to some PyPI packages.

I'm going to try and make available, probably by adding to rdflib utils, a DefinedNamespace script that people can use, so we can compare that with your BRICK script eventually.

OK, well this passes tests and looks fine to me so I'll merge in, without requiring further reviews. We may eventually split many namespaces off into a separate repo but, for now, I'll merge them into the core.