Inside temperature is always at least 0.1 K higher than outside temperature

This is one outcome of #62 (closed): to be more realistic, the outside temperature cannot go above the inside temperature minus 0.1 K. The absolute value in the formula is hence taken out. This gives more critical results (i.e. higher R0) for the summer months, but it is more physical than the previous implementation (although still with some arbitrariness). The tests results for R0 in June had hence to be modified.

That's the new concentration profile (full window opening in June):

... compared to the previous concentration profile (full window opening in June):