[FIX] stock_account: stock_history report

* shadowing of "fields" import in the read_group function as it receives
  a "fields" arg. As we have to use fields.Datetime in this method,
  whe choosed to reimport it as "fieldsDatetime" to use it.
* cast not_real_cost_method_products.ids list to tuple, because
  psycopg2 only accept tuple for "IN" condition.