Biological decay for low and high indoor RH

Today the biological decay is constant with a half life of 1.1h

We know now that the effect of central heating during the winter dries the air (lower RH) and increases the halflife to 3.8 h - see paper

Propose change to:

if self.event_month[:3] = ["January", "February", "March", "October", "November", "December"] halflife=3.8 else halflife=1.1