Draft: Adding tool for temperature initialisation

For the temperature initialisation a new tool "InitialisationTool.hpp" is now available within the src/terraneo/helpers directory. Temperature initialisation is performed superimposing a distinct amount of white noise or temperature deviations from spherical harmonics onto the reference temperature profile (currently adiabatic profile). This should allow us to modularise initialisation procedures in convection apps and lets us stay closer to master according to issue #243 .