Make itkStatismoConfig.h first included header.

Fix needed to avoid version conflicts due to duplicate headers, when statismo_ITK is used together with an external hdf5 installation.
Additional include guard to prevent HDF5Cpp.h to be included when itkH5Cpp is used.
Avoid the use of ITK's HDF5 libraries for vtk representerTests.
Add .cxx and .cpp files to install files
Update STATISMO_INCLUDE_DIRS to reflect new build/install procedure

1) Added include directories of eigen and boost
2) Changed include path of statismo header files