Device CCA code should be able to return a cell-measurement map

[stephenswat]

Currently, our device CCA algorithms convert cells directly to measurements, without the intermediate cluster data. For some debugging use cases, we will need to have this data, as we want to be able to map cells to measurements and vice versa. This can be easily implemented by optionally returning a union-find list from the device CCA algorithms.

Tagging @paradajzblond; assigning myself to implement this.