Create capacity conversion group

[DCEW]

Capacity conversion will require a custom aggregation of results, similar to 'detailed results'.

In order to do this, we need to create a column "capacity_conversion_group" in the various datasets

[tomjemmett]

some additional logic will be needed for the OP groups, they are meant to be split by F2F/Tele, but we combine those rows together (counting each type in their own columns). So, I've had to use a generic group for now.