Docs: How to QA Occurrences

[florianm]

Problem

Explain all workflows related to QAmixin in docs (high level as own chapter), add as functional tests, compare to and close off requirements, generate reference docs from functional tests.

• Status name and meaning, symbolisation (colour)
• Preconditions (currently none),
• role permissions (data curator etc).

Feature

See dbca-wa/wastd#299 dbca-wa/wastd#291