Vignette advanced audit log parsing

[florianm]

Feature

ODK Central will add submission editing to the front end, see release Block 12 criteria.

Central stores edited records as new submissions of the same record, and renders a diff between submissions in the per submission audit feed (a detail page for a submission).
The information about individual edits to records will be available through the API and documented eventually.
Then we should add a vignette with a few worked examples on parsing and reviewing the submission edit audit logs.