Refactoring the heat equation.

examples/heat-equation/heatEquationSolver_impl.h

examples/heat-equation/tnlDirichletBoundaryConditions.h

examples/heat-equation/tnlDirichletBoundaryConditions_impl.h

examples/heat-equation/tnlLinearDiffusion.h

examples/heat-equation/tnlLinearDiffusion_impl.h

src/config/tnlConfigDescription.cpp

src/implementation/mesh/CMakeLists.txt

src/implementation/mesh/tnlGrid1D_impl.h

src/implementation/mesh/tnlGrid2D_impl.h

src/implementation/mesh/tnlGrid3D_impl.h

src/implementation/mesh/tnlGridCellNeighbours_impl.h

src/implementation/mesh/tnlTraversal_Grid2D_impl.h

src/implementation/mesh/tnlTraversal_Grid3D_impl.h

...mplementation/schemes/diffusion/tnlLinearDiffusion_impl.h

src/mesh/CMakeLists.txt

src/mesh/tnlGrid.h

src/mesh/tnlGridCellNeighbours.h

src/solvers/pde/tnlExplicitUpdater.h

tools/src/CMakeLists.txt

tools/src/tnl-init.cpp