doc: dev guide: add informal spec about individual contexts aka vocabularies
Upgrade stable version to 2.0.4
UI/UX: context => vocabulary revamp step 1/3

- rename all instances of '(meta_)context' to 'vocabulary'
- implement new unified design (combines context, vocabulary and abstract)

still missing:
- some counting queries
- optimize/consilidate existing queries
- fix tests
- polish (step 3)