Add option to assign output coordinate values from attributes in area_overlap

[jucordero]

The area overlap returns a 2D array with the corresponding area for each combination of values from two segmentation maps.

The coordinate values assigned to each dimension of the output map are the unique values in the segmentation maps by default, or an input array of dimension values set by the dim_left and dim_right keywords.

It would be good to have an automatic output option which would select the values to use in the coordinates from a well defined attribute entry in each array.