Showing the areas of the labeling groups

[ds2268]

This is a continuation of issue #125

For the areas, it would be good to have them for all, but this is specific. In our case, we have some bigger regions in which cells are labeled and it's good to know for the pathologists what is the area (e.g. hot-spot region). It needs to be of sufficient size to be sound. This information is reachable, as you mentioned, but it's hidden and not that useful. I agree that presenting the area at each element would hinder the usefulness in some other cases where you have some segmentation of thousands of objects where displaying the area would not make sense. One option is to have a flag where you can enable or disable displaying the area for each element, but by default just have a total area displayed per group (and only if polygon or rectangle). This needs to be aligned with other UCs to have a common benefit.