Adding more combinations in spd-spd dI/dV method

[ondrejkrejci]

Some of the spd vs. spd orbitals are clearly missing, as the formulas are simply too long, to be rewritten properly.
One could easily use the numerical derivation (with amplitude of something like 0.01 Å) as it is done in the IETS C++ procedure here:
https://github.com/Probe-Particle/PPSTM/blob/master/cpp/ProbeSTM_spd.cpp#L200
To add those combinations for dIdV procedures, that are missing.