Reimplementing the grid.

examples/heat-equation/tnlNeumannBoundaryConditions.h

examples/heat-equation/tnlNeumannBoundaryConditions_impl.h

examples/heat-equation/tnlZeroRightHandSide.h

examples/heat-equation/tnlZeroRightHandSide_impl.h

src/implementation/mesh/tnlGrid1D_impl.h

src/implementation/mesh/tnlGrid2D_impl.h

src/implementation/mesh/tnlGrid3D_impl.h

src/implementation/schemes/tnlFiniteDifferences_impl.h

src/mesh/CMakeLists.txt

src/mesh/tnlGrid.h

src/schemes/tnlFiniteDifferences.h

tools/src/tnl-diff.cpp

tools/src/tnl-discrete.cpp

tools/src/tnl-discrete.h

tools/src/tnl-view.cpp