Add warning in VoronoiRegionalizer if not every seed point is inside its region

[RaczeQ]

When seed points are really close to each other, the regions sometimes contain 2 points while others contain 0. The boundary of the regions when mapped from spherical geometry to WGS84 is not 100% fool-proof. The parameter max_meters_between_points steers the precision of this mapping.
The method should show a warning if this situation happens and suggests increasing the precision. Maybe implementing a foolproof solution should be explored (with an optional flag, since it might be slow).

[RaczeQ]

Example on the map: