Starts a new terraneo module
As discussed in the last developer meeting it is time, in light of soon to come extensions, to start with a separate terraneo module. This is intended to house code specifically addressing the needs of running mantle convection models with HyTeG. This commit starts with the new module and relocates the SphericalHarmonicsTool into it.
src/hyteg/numerictools/SphericalHarmonicsTool.cpp → src/terraneo/sphericalharmonics/SphericalHarmonicsTool.cpp
src/hyteg/numerictools/SphericalHarmonicsTool.hpp → src/terraneo/sphericalharmonics/SphericalHarmonicsTool.hpp