Refs #6078, prepend numeral index to each column in pivotted datatable.

core/API/DocumentationGenerator.php

core/DataTable/Filter/PivotByDimension.php

tests/PHPUnit/Core/DataTable/Filter/PivotByDimensionTest.php

tests/PHPUnit/Integration/PivotByQueryParamTest.php

...PlaysNiceWithDataTableMaps__Referrers.getKeywords_day.xml

...amWorksWithColumnLimiting__Referrers.getKeywords_week.xml

...ByParamWorksWithCsvOutput__Referrers.getKeywords_week.csv

...ParamWorksWithJsonOutput__Referrers.getKeywords_week.json

...thReportWhoseSubtableIsSelf__Actions.getPageUrls_week.xml

...eWhenSegmentUsedInRequest__Referrers.getKeywords_week.xml

...tCreatesCorrectPivotTable__Referrers.getKeywords_week.xml

...ntireHirearchyIsNotLoaded__Referrers.getKeywords_week.xml