[Feat] r.kappa: improve output and add User's and Producer's accuracies

[neteler]

r.kappa lacks:

• User's and Producer's accuracies
• Output in CSV
• sort output differently:
  • arrange user and producer accuracies and omission and commission around the error matrix instead of the summary columns
• add notes to "map1" and "map2" to explain what that means (more user friendly)

For a working solution, see https://github.com/OSGeo/grass-addons/blob/master/grass7/raster/r.confusionmatrix/r.confusionmatrix.py

[neteler]

Note: for GRASS GIS 8, consider to rename r.kappa to r.validation or the like (as per OSGeo/grass-addons#109 (comment))

[marisn]

r.kappa now supports JSON output. I'd guess CSV output is not required any more. See: #2666

[neteler]

Excellent, solved since G83:

see here:

                "producers_accuracy": [57.1429, 0.0, 100.0, None, 100.0, 66.66666],
                "users_accuracy": [100.0, None, 80.0, 0.0, 100.0, 50.0],
                "conditional_kappa": [1.0, None, 0.742857, 0.0, 1.0, 0.400],