Fix case of Infinits and NaN in statistics
Merge pull request #188 from obiba/aggregation-statistics

Fix case of Infinits and NaN in statistics
Variable header in harmonization CSV
Merge pull request #189 from obiba/harmonization-csv

Variable header in harmonization CSV
Always respond to data aggregation query, even if statistics could not be retrieved from opal
Parallel query for statistics on dataschema variable
Merge pull request #190 from obiba/parallel-statistics

Parallel statistics