Flood Fill merging

[jara001]

Currently tested curvature-based selection (and segmentation) uncovered another issue with the used segmentator.

When the selection is uneven, it can happen, that one segment 'gets trapped' because of another segment spreading outside its proper area. This can be show, e.g., in the following image:

{
    "_version": 2,
    "_comment": "Experiment with MM and Curvature2.",
    "loops": 10,
    "groups": -3,
    "interpolator": "cubic_spline",
    "segmentator": "flood_fill",
    "selector": "curvature2",
    "selector_args": {
        "plot": false,
        "point_distance": 0.1,
        "sampling_distance": 1.0,
        "peaks_height": 1.0,
        "peaks_distance": 16,
        "peaks_bounds": 8,
        "peaks_filling": 7.0
    },
    "cascade": [
        {
            "algorithm": "matryoshka",
            "budget": 3000,
            "layers": 5,
            "criterion": "profile",
            "criterion_args": {
                "overlap": 100
            },
            "criterion_init": {
                "_dummy": 0
            }
        },
        {
            "algorithm": "matryoshka",
            "budget": 1000,
            "layers": 5,
            "criterion": "profile",
            "criterion_args": {
                "overlap": 100
            },
            "criterion_init": {
                "_dummy": 0
            }
        }
    ],
    "start_points": "ng_start_points_torino2.npy",
    "valid_points": "ng_valid_points_torino2.npy",
    "logging_verbosity": 2,
    "hold_map": true,
    "plot": true,
    "plot_args": [
        {
            "_figure": {
                "function": "axis",
                "_args": [ "equal" ]
            },
            "trackPlot": [ "@track" ],
            "pointsPlot": {
                "_args": [ "@result" ]
            }
        },
        {
            "pointsPlot": {
                "_args": [ "@result" ]
            },
            "pointsScatter": {
                "_args": [ "@rcandidate" ]
            }
        }
    ],
    "prefix": "matcur2"
}