[material][components] add temperature dependent vaporization enthalpy to gas enthalpy of simpleh2o

What this MR does / why does DuMux need it: This adds the vaporization enthalpy to the gas enthalpy. This is needed for components that can have a phase change. A temperature dependence on tRef is introduced according to a simple formula found in literature.

Remark: This is consistent with constant component as both calculate the gas enthalpy as gasHeatCapacity(temperature, pressure)*(temperature - tRef) + vaporizationEnthalpy(). However, for constant component the vaporization enthalpy is an input value (constant) while simpleh2o uses the calculation based on literature.

Which issue this MR fixes: fixes #1013 (closed)

Todo:

• check if any test is influenced by this. so far i could not find one