Sometimes you want stale data right away, then refresh it async.
This adds `findStale` to the store for that case. If it returns
an object with `hasResults` you can get the `results` and display
them.
It also returns a `refresh()` method to freshen up the stale data.
To enable `localStorage` support for stale data, just include the
mixin `StaleLocalStorage` into an adapter for that model. This
commit includes a sample of doing that for `Notifications`.
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