Add feature to automatically set reference energy for Davis Products EOS

The Davis Products EOS is most often used in combination with a reactants EOS to model reactive flows. For a detonation wave to be self-propagating, the Rayleigh line extending from the initial conditions of the reactants needs to be tangent to the release isentrope of the products at the CJ point. Most often, we want this CJ isentrope to the reference isentrope for the Davis EOS, so it makes sense to be able to automatically set the reference energy of the products EOS automatically in order to achieve this tangency condition.

This will require an iterative procedure at setup that will could look something like this:

1. Find bounding points on the reference isentrope where the slope of the Rayleigh line is larger than and smaller than the slope of the isentrope.
2. Use a bounded root finding method to iteratively find the point where the slope of the Rayleigh line equals the slope of the reference isentrope
3. Calculate the energy of the CJ point given the Rayleigh line and then subtract the energy of the reference isentrope at the CJ point to calculate the appropriate energy offset.

This procedure should be done with an arbitrary reactants reference energy.