Review item SRS stage history

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I'd like to be able to have a history of the SRS stage individual review items have been in over time. This would allow for a few really cool features:

1. A chart showing an individual items progress over time on its page.
2. Heuristic for items that have had a "fall from grace", for example something that's trending down from master/enlightened back to apprentice. This could probably be scrapped in favor of running with the "leech item" heuristic on the todo list.
3. Charts showing aggregate history of item type per SRS stage over time (5 charts), as well as the reverse, SRS stage per item type over time (3 charts). This would best fit in a dropdown box on the search page, where aggregation can be done on matching items, and extraneous graph types can be hidden (ex. a search that only yields apprentice items wouldn't show the other 4 SRS stage charts)

The big asterisk here is that all of this would have to be handled in local storage, which is tragic but worth it IMO.

[Lemmmy]

No new storage should be necessary; the app already has the review objects, but they're effectively useless until WaniKani re-enables the API—the app tracks them itself, but it can't get your reviews from other devices or when signing back in. Nonetheless, 1 and 3 can be done with the review objects, and 2 can be done with the review statistic objects using the leech tracking formula described here (code example from Smouldering Durtles).