ITK spatial objects in OTB

ITK spatial objects, and in particular itk::LineSpatialObject, are only used in a few classes of the OTB: the module Core/spatialObjects and the filters using this module:

• FillGapsFilter
• LocalHoughFilter
• ExtractSegmentsImageFilter
• LineSpatialObjectListToRightAnglePointSetFilter
• HoughTransform2DLinesImageFilter

The module and those four filters are not used anywhere else in OTB. In OTB we already have OGR to model geometries, so I think otb::SpatialObjects should be removed and the filters should be updated to use ogr instead (or maybe removed if they're not useful anymore)

This was already discussed in #1763 (closed)

in ITK 5.0, there is a major API change for spatial objects, so we need to make a decision about otb::spatialObjects as soon as possible.