Add documentation on the vocabulary server

[CecSve]

Add documentation for the vocabulary server on relevant pages. The main page should probably be data processing and quality checks.

• add version documentation (How can one define remapping from one vocabulary version to another? vocabulary#132) (pending development)
• add documentation on roles and scopes for external vocabulary curation (pending development)
• make a section for recommended controlled vocabularies in data publishing
• add information on vocabulary status: 'In use', 'deprecated', 'testing' labels or indications on vocabularies vocabulary#155 (pending development)