refs #1700: new metrics min_time_generation, max_time_generation

 * DataTable_Row::sumRow has a new parameter $aggregationOperations which allows treating columns as min or max (not only sum)
 * The aggregation operations can be set on any data table or passed to ArchiveProcessing_Period::archiveDataTable()
 * The Actions plugin uses the mechanism to aggregate the new metrics as min and max
 * The metrics are in the API output but not in processed reports
 * The min/max values are shown in the tooltip that appears when hovering the average generation times
 * Integration test updates