[material] Several fixes for effective thermal conductivity laws

* Fix documentation for Johansen
* Deprecate ThermalConductivitySomerton in favor of ThermalConductivitySomertonTwoP and ThermalConductivitySomertonThreeP
Before they couldn't be included in the same simulation
* Deprecate Dumux::ThermalConductivitySimpleFluidLumping it's the same as Dumux::ThermalConductivityAverage but
the latter works for n fluid phases instead of only two fluid phases