Add toString() in Node and Segment2D
Add isStrictlyAtLeft() to Segment2D
add linSpace2D() in TestTool
add getChainsHeads() in polygon2D
make PerturbationSearchMethod inner class or Model2D works when 'center' is of a boundary head or rear

  - also extract checkPerturbedCenter()
Make and test EnsureNodesNode nodes influcence domain radius calculator