Introduce totals support in visualizations and their conversions #1210

• Bucket contains the totals field
• New AFM execution conversion methods with totals support:
  • VisualizationConverter.convertToResultSpecWithTotals
  • VisualizationConverter.convertToAfmWithNativeTotals
  • VisualizationConverter.convertToExecutionWithTotals

Old conversion methods (without totals support) must be kept as they are for the backward-compatibility.