Unify the Domain, Cell and Particle classes.

[v0dro]

Currently @wawando 's Eigenvalue factorization code uses a Domain, Cell and Particle class which are different from the Hatrix trunk. We need to unify them and use the same classes in all the examples. These must originate from the Hatrix trunk.

The following needs to be resolved in order to make this happen:

1. Remove pointers from the Cell class.

In order to integrate @wawando 's code with the trunk Hatrix, changes can be made in the following order:

Particle class integration into all the examples

1. @wawando uses Body instead of Particle.
2. Remove the Body class from common/ and replace all occurrences with Particle.
3. The end result is to completely get rid of Body and merge it into Particle.
4. Final result: Remove this line and remove the Body.hpp file.

Cell class integration into the all the examples.

Cell from common/ is used in the following codes:

• https://github.com/rioyokotalab/Hatrix/blob/dev/examples/common/Domain.hpp
• https://github.com/rioyokotalab/Hatrix/blob/dev/examples/common/functions.hpp
• https://github.com/rioyokotalab/Hatrix/blob/dev/examples/Dense_EV.cpp
• https://github.com/rioyokotalab/Hatrix/blob/dev/examples/Dense_EV_sym_mpi.cpp
• https://github.com/rioyokotalab/Hatrix/blob/dev/examples/H2_strong_CON.cpp
• https://github.com/rioyokotalab/Hatrix/blob/dev/examples/H2_strong_CON_sym_ID.cpp
• https://github.com/rioyokotalab/Hatrix/blob/dev/examples/H2_strong_EV_sym.cpp
• https://github.com/rioyokotalab/Hatrix/blob/dev/examples/H2_strong_EV_sym_mpi.cpp
• https://github.com/rioyokotalab/Hatrix/blob/dev/examples/H2_strong_EV_sym_mpi_ref.cpp
• https://github.com/rioyokotalab/Hatrix/blob/dev/examples/H2_strong_EV_sym_nodep.cpp
• https://github.com/rioyokotalab/Hatrix/blob/dev/examples/H2_strong_LDL.cpp
• https://github.com/rioyokotalab/Hatrix/blob/dev/examples/H2_strong_LDL_nodep.cpp
• https://github.com/rioyokotalab/Hatrix/blob/dev/examples/H2_strong_PO.cpp
• https://github.com/rioyokotalab/Hatrix/blob/dev/examples/H2_strong_PO_nodep.cpp