Make doUpdate/doInitialize protected to be able to overload them
Add ParticleReference index accessor

This is useful in SPH to store the particle's indices in the grid...
Add SphRepresentation
Add SphRepresentation unit test
Add SphRepresentation render test
Add SphRepresentation serialization
Complete SphRepresentation serialization + add unit test
Add Blocks::TransferParticlesToPointCloudBehavior + unit test

also refactor the SphRepresentation render test to use this behavior.
SPH render test clean up
Assert on Source/Target in TransferParticleToPointCloudXXX::doInitialize + test
Make Kernels non-templatized methods + fix coding standard method naming
Shorten set/get methods Density"Reference"/SurfaceTension"Coefficient"

Method rename set/getDensityReference -> set/getDensity
Method rename set/getSurfaceTensionCoefficient -> set/getSurfaceTension
Rename member variable m_surfaceTensionCoefficient - > m_surfaceTension

The member variable m_densityReference remains as is to emphasize the fact that the density varies dynamically per particles and pressure is computed relative to this "reference" density.
Use doxygen tag /throws to notify exceptions
Optimize/clean up computeDensityAndPressureField()
Optimize/clean up method computeNormalField()
Optimize/clean up method computeAccelerations()
Replace all methods signature X(void) to X()
Fix some Blocks static build failing because of missing Particles library.
Fix bug in ParticleReference, getter should not return an lvalue

const Eigen::VectorBlock<Vector, 3> u; // u is accessible as a lvalue and the content of the vector can be modified
The proper syntax is:
const Eigen::VectorBlock<const Vector, 3> u; // The content is defined as a const Vector and therefore is not accessible as a lvalue
Push the Sph acceleration member variable in the ParticleState

Now, the ParticleState contains all the degrees of freedom and their time derivative (velocities and accelerations).