Segmentation: Add functions to work on vectors of cellBoundaries instead of uniform cellSizes

Treatment of edge cases (see comments in the code as well)
If we are close to the lower bound, we assume it is in the bottom
Include upper boundary to the segmentation
If the value is below or above the lowest or highest, throw exception, this means the segmentation is always bound by values we give it

Need to subtract 1 from the result, because upper_bound works that way