Add periodic boundary conditions in Exemples ; Check periodic boundary conditions. ../Tests/Kernels/testSphericalDlpolyAlgorithm.cpp

Change WARNING in STATUS (debug)
Remove value 0, 1 to FParticleType enum

Fix bug with constexpr ans string
New Macro for API2 of ScalFMM for cells and kernels classes

	  const in constexpr
	 @param in @tparam for template in doxygen files
....

Remove white space and align data
Code improvements (for cppcheck)
Add comments

In files that may be used without StarPU.

This allows altering the LICENCE text without changing all files. It should
avoid merge conflicts in the future.

Add
  - CutOffKernel which uses the matrixkernel class in the P2P Operator
  - CutOffAlgorithm to explain how we can use scalFMM with only cutOff method. The Octree dos not contain any local or multipole values.