Moved processed metrics computation to DataTableGenericFilter, removed new...

Moved processed metrics computation to DataTableGenericFilter, removed new filters & implemented as methods in Report to avoid confusion regarding re-use, allow adding processed metrics as DataTable metadata and use this to rewrite AddProcessedMetrics filter, correct name of Metrics::getMappingFromIdToName function, added placeholder AggregatedMetric class for future, revise Metric/ProcessedMetric hierarchy (add methods for translation/etc.), allow .get API methods to use metadata to automatically figure out which columns to select, get EcommerceOrderWithItemsTest to pass.