Make WFAssemblier more complex
  - add setNodesNum, setMatrixDense, setConstitutiveLaw, prepare isUpperSymmetric
  - change and test penaltyWFAssemblier, LagrangeWFAssemblier accordingly
    + also correct the package name of their tests class
  - add prepareAssemblier() to WFAssemblier
Extract prepare() from WFAssemblier into a new interface

  - NeedPreparation
Polygon2D:

  - add min and max segment length getter
  - rename fractionize() parameter, a non-functional change.
PolygonProject2D:

  - make final protected initPolygonProject2D
  - rename the getter to setSemgnetQuadratureDegree
Extract RectangleProject from TimoshenkoStandardProject