Tabulate by Batch, and readiness for Tabulate By X

[artoonie]

Request for comment on language. As a noun, I call it a "a tabulate-by field" As a verb, I call it "Tabulate By Field"

I can imagine preferences for other names, by "Tabulate By Pivot" or "Tabulate By Metadata Field" or something else, but "Tabulate By Field" seems sufficiently clear to me. Thoughts? Any other words that may reduce ambiguity?

Closes #807

[artoonie]

@yezr this has been lightly tested but I could use some help gathering test data, test configurations, and checking edge cases.

[artoonie]

@tarheel all comments are addressed!