Add calibration checks to density and viscosity models

[kaylai]

@simonwmatthews I've added the density and viscosity code in and will push that to pip in v1.1.0 soon. Since there is only one model for density and one for viscosity, I did not use a model_classes file like we did for the volatile solubility models. I'm unsure of the best way to add calibration checks for these models. Would you mind taking a look?

[simonwmatthews]

I think the best way to do it would be to have all the calibration check code sitting directly in the ThermoCalculate classes, i.e., the equivalent code to models.magmasat.check_calibration_range() could go directly into thermo.thermo_calculate_classes.calculate_liquid_density.check_calibration_range(). Or have I missed something?