1) rename table da_vsturn to da_vst 2) implement fit of davst (determine b1 as average over seeds -> b1mean, fit data for each seed for fixed b1mean by scanning of kappa and using the kappa with the minimal residual), the fit data is stored in the new tabl da_vst_fit
add test for da vst fit and implement save_davst_fit to save the da vst fit data in a file