added posibility to use est_t_max for time adaptivity. The time error may now...

added posibility to use est_t_max for time adaptivity. The time error may now be defined as est_t_combined =sum_fac*est_t_sum + max_fac*est_t_max. Default is sum_fac=1 and max_fac=0. Thus, by default adaption is working as before.