Compare statement revisions

[gbp]

We should store the revision after a statement has been actioned. This can be compared with this schema:version revision from the SPARQL query to better distinguish between “We updated this, but aren’t seeing that reflected yet”, and “We updated that, but there have since been further updates that have changed something significant” cases.

With this we should improve the “There were no ‘position held’ (P39) statements on Wikidata that match the actioned suggestion” message which sometimes occurs.

We might want to consider increase the grace period where we force a recently actioned statement in the done state to combat the WDQS update lag.

[tmtmtmtm]

https://phabricator.wikimedia.org/T199228 is related to this, wrt lag times (summary: several hours is normal/to be expected; several days is problematic but does happen)