New function lots_by_location
In Lot, implement
def lots_by_location(cls, location_ids, lot_ids=None, with_childs=False)
It will prepare params and context to call 'products_by_location()' and parse
the result to return a two levels dictionary: first level with Locations ID as
keys and second level with Lots ID as keys.
It will be implemented in #review845002