KaliVeda with units!

Replace all variables which represent dimensioned quantities (energies, momenta, area density, cross section, ...) with new types which associate a numerical value and associated units, and also implement all possible conversions between units. Make the internal code 'unit safe', but make the user interface backwards compatible so that user code just using 'normal' variables (Double_t, TVector3 (?)) still compiles & works, but without any guarantee of 'unit safety'.