Serialization

• clean a bit NodeBase class.
• wip serialization of NodeBase that exemplify the 'intrusive' serialization (Serializer class member) + test.
• wip serialization of Eigen types (binary only) + test.
• serialization TimeStamp + test.
• serialization entry-point object is referred by typeid.

src/serialization/cereal/CMakeLists.txt

 INCLUDE_DIRECTORIES(${CMAKE_CURRENT_SOURCE_DIR})
 
 SET(HDRS_SERIALIZATION ${HDRS_SERIALIZATION}
+    ${CMAKE_CURRENT_SOURCE_DIR}/serialization_eigen_core.h
+    ${CMAKE_CURRENT_SOURCE_DIR}/serialization_eigen_geometry.h
+    ${CMAKE_CURRENT_SOURCE_DIR}/serialization_eigen_sparse.h
+
     ${CMAKE_CURRENT_SOURCE_DIR}/serialization_local_parametrization_base.h
     ${CMAKE_CURRENT_SOURCE_DIR}/serialization_local_parametrization_homogeneous.h
     ${CMAKE_CURRENT_SOURCE_DIR}/serialization_local_parametrization_quaternion.h