MOLLI correction factor

[alexdaniel654]

The equation at L298 of mapping/t1.py can simplify from correction_factor = (self.m0_map * self.eff_map) / self.m0_map - 1 i.e. $cf = \frac{M_0 eff}{M_0 - 1}$ to correction_factor = 1 - self.eff_map.