cubicweb-dataio #2573926 Implement Massive Store [done]

The Massive Store is a CW store used to push massive amount of data using pure SQL logic, thus avoiding CW checks. It is faster than other CW stores (it does not check eid at each step, it use COPY FROM method), but is less safe (no data integrity securities), and does not return an eid while using create_entity function.

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closed by#201daffb65b8 Add the massive (CSV) import store, closes #2573926