Implement a FluidPropertyWrapper class that handles REFPROP mixtures

[fwitte]

Some considerations to be collected below

• Td_bp then needs to refer to Q=0 in case of subcooling and Q=1 in case of superheating
• A method to access bubble and dew points would a good addition in this context, it could also be propagated to the CoolPropWrapper and use Q=0 or Q=1 respectively for consistency reasons, even if CoolPropMixtures are not supported.
• minimum and maximum value of enthalpy/pressure seem to not work out of the box. So implementing a REFPROPMixtureWrapper handling those cases would be a reasonable idea, and for the convergence helpers in the iterations of the problem, the call for value boundaries should be delegated to the fluid property functions (and wrappers).