WS does not support measure filter applying for the row

[buchslava]

The reason for the issue is due to WS functionality: WS does not support measure filter applying for the row. It supports filter applying for column (separate measure) only. Let me explain...

Imagine, we have next filter and next result for a dataset (datapoints selection):
Filter is empty {}
Result is

geo | time  | life_expectancy | population
arg  | 1991 | 72                      | 900000

An another case for same dataset:
Filter is { $or: [ {population_total: {$gt: 10000}}, {life_expectancy_years: {$gt: 30, $lt: 70}} ] }

Result for DDFCSV reader is

geo | time | life_expectancy | population
arg | 1991 | 72                     |  900000

because 72>70 is false OR 90000>10000 is true -> result is true

Result for WS reader is

geo | time | life_expectancy | population
arg | 1991 | null                    | 900000

because WS applies the filter for each measure separately and merges result after that

I guess it's incorrect in accordance with https://docs.google.com/document/d/1olFm-XXjWxQ4LrTCfM42an6LbjbIgnt__V1DZxSmnuQ/edit# (Filter which affects which rows of the selection will be included in the response. This filter is a subset of MongoDB query operators)