The beginnings of a data store

This is admittedly a wimpy data store -- it's more like a caching layer. But it does pull a lot of logic out of ExaminePage, which is a step in the right direction. It's a nice performance win, to boot.

Highlights:
- Adds a bunch of tests for things like sorting & filtering.
- Pulls lots of data logic out into a separate module while miraculously not breaking said tests.
- Replace `everyOver` + `equals` with `_.isEqual`, which is simpler, clearer & amounts to the same thing.
That is a great question. Somehow (I couldn't immediately figure out the channel) `idiogrammatik` is leaking out into the global namespace when I run in-browser. What's more surprising is that this works under node/Jest. In any case, fixed.