Automatic Tests Generation

Updates:

• Implemented function generate_column_tests() to generate similar tests for many columns automatically

Dataset Null-related tests

• Implemented TestNumberOfNulls to replace TestNumberOfNANs and TestNumberOfNullValues
• Implemented TestShareOfNulls
• Implemented TestShareOfColumnsWithNulls
• Implemented TestShareOfRowsWithNulls
• Implemented TestNumberOfDifferentNulls

Column Null-related tests

• Implemented TestColumnNumberOfNulls to replace TestColumnNumberOfNullValues
• Implemented TestColumnShareOfNulls to replace TestColumnNANShare

Fixes:

• Fixed metric duplication to reduce an amount of calculations while building TestSuites (basically, now same metrics from the one test suite are not recalculated multiple times)
• Implemented NAN filtering for all dashboards in way, that each column is filtered separately