Refactoring functions.

src/functors/tnlExpBumpFunction.h

src/functors/tnlExpBumpFunction_impl.h

src/functors/tnlFunctionDiscretizer.h

src/functors/tnlFunctionDiscretizer_impl.h

src/functors/tnlSinBumpsFunction.h

src/functors/tnlSinBumpsFunction_impl.h

src/functors/tnlSinWaveFunction.h

src/functors/tnlSinWaveFunction_impl.h

src/functors/tnlTestFunction.h

src/functors/tnlTestFunction_impl.h

src/operators/diffusion/tnlExactLinearDiffusion.h

src/operators/diffusion/tnlExactLinearDiffusion_impl.h

src/problems/tnlHeatEquationEocRhs.h