Provide a way for custom visuals to get subtotals in their dataviews.

[pbiideas1]

Since the only way currently available to request for subtotals to be provided in dataviews is by implementing a customizeQuery () method in the visual's plugin, which is, as far as I know, not possible under the custom visuals sandboxing, I think it would be extremely helpful if an alternative way to get the subtotals in the dataview would be provided; E.g. by setting the SubtotalType directly in the visual's capabilities.dataviewMappings' role mappings.