Fix ML types in CLI

Fix decoding of JSON values for ML model types
Fix intermittent test failure in TestRowOperators
Use StandardType constants in QueryResults
Remove extra space in LearnLibSvmClassifierAggregation
Save conf so that superclass methods have access to it via getConf()
Fix for row number window function optimization
Update approx_distinct to use more precise airlift HLL implementation
Allow specifying standard error for approx_distinct agggregation function