fix for dist_quantile all NA s

[dsweber2]

Checklist

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  dajmcdon.
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Change explanations for reviewer

Magic GitHub syntax to mark associated Issue(s) as resolved when this is merged into the default branch

• Resolves quantile() method for dist_quantiles should produce NAs as needed, not error #414

[dsweber2]

This actually broke b/c of some changes to epiprocess' interface in an unrelated vignette. I added a fix for that. It changes the name of the slide column from cr_7dav to case_rate_7dav