Make vocabularies extensible

[sarafalamaki]

We'll need additional vocabulary elements for each deployment. How do we plug them in? Currently we have things like BizStep and Disposition as types, so adding to them isn't possible. Should they be type classes instead?

Original Author: fal05c

(Moved with github-migration-0.1.0.0 (package github-migration-0.1.0.0 revision df9f38b))