Update cooling grackle

Still need to deal with conflicts, I will assign this merge request when the code will be ready.

Basically, I have updated the code done by @yvesrevaz and checked it.

After this merge request, I am planning to improve the code (not a big fan of having a cooling_wrapper file), pass from grackle v2 to v3 and change the way grackle compute the cooling rate (currently only reading a table, in the future it would be possible to compute the chemical network on the fly).

examples/CoolingBox/coolingBox.yml

@@ -39,3 +39,10 @@ LambdaCooling:
   mean_molecular_weight:       0.59       # Mean molecular weight
   hydrogen_mass_abundance:     0.75       # Hydrogen mass abundance (dimensionless)
   cooling_tstep_mult:          1.0        # Dimensionless pre-factor for the time-step condition
+
+# Cooling with Grackle 2.0
+GrackleCooling:
+  GrackleCloudyTable: ../CloudyData_UVB=HM2012.h5 # Name of the Cloudy Table (available on the grackle bitbucket repository)
+  UVbackground: 0 # Enable or not the UV background
+  GrackleRedshift: 0 # Redshift to use (-1 means time based redshift)
+  GrackleHSShieldingDensityThreshold: 1.1708e-26 # self shielding threshold in internal system of units