Updated postprocessing of shortFuel case, and uncommented thermochimica calculation lines in coolant corrosion calculation

Likely unphysically high slope of density of fuel salt at low temperatures causing OpenFOAM run to not converge, so instead of linear extrapolation, I used constant

Finished short fuel case, and wrote case for full length fuel simulation: wrote a new full length mesh, updated thermophysical properties, temperature profile, boundary conditions, and calculated polynomial fits from final properties

Based on the automatic case generation in CFDOF, I believe the temperature gradient might actually just be the heat flux itself (in W/m^2), and perhaps there's some rescaling in OpenFOAM, although I'm not sure how this works

Added a notebook showing the calculation of the temperature gradient for OpenFOAM, and updated default values of the temperature field and the output value based on the updated scoping calculations