Splitting the grid traversing into boundary and interior entities traversing.

src/implementation/matrices/tnlMatrixSetter_impl.h

src/implementation/mesh/tnlTraversal_Grid1D_impl.h

src/implementation/mesh/tnlTraversal_Grid2D_impl.h

src/implementation/mesh/tnlTraversal_Grid3D_impl.h

src/implementation/solvers/pde/tnlExplicitUpdater_impl.h

...mplementation/solvers/pde/tnlLinearSystemAssembler_impl.h

src/mesh/tnlTraversal_Grid1D.h

src/mesh/tnlTraversal_Grid2D.h

src/mesh/tnlTraversal_Grid3D.h