Add EOS temperature from entropy floor

This merge request fixes a difference we implemented differently in SWIFT as compared to EAGLE. Instead of calculating the EOS temperature from the star formation EOS we need to calculate this from the entropy floor, this merge request does that. I also have run the idealized disk without problems, it produces the same result. threshold density (numb/cm^3) is around 0.03 for solar, that still has a temperature above the threshold given by around (0.03/0.1)^(1/3)8000 K10^.5 = 17000 K, so in the case of my disk, it produces exactly the same result as before. Any comments on the code?