Correctly read in critical accretion rate in SPIN/JET BH scheme

The critical Eddington ratio parameter, mdot_crit_ADAF, is used to switch between the thin accretion disc/thermal feedback to the thick disc/jet feedback. In previous versions of the model, this was connected to the accretion viscosity parameter alpha_acc, based on theory. While we still know there should be a connection, it is a bit more flexible to have both parameters as explicit ones in the code

I now correct this to read in mdot_crit_ADAF from the parameter file. The suggested value is also changed to 0.03 instead of 0.01 in the parameter files (we know it's at a bit higher Eddington ratios than 0.01). A value of 0.03 is also more consistent with the current choice of alpha_acc, which is 0.2.