Torches: Reduce light source level from 13 to 12

Torches: Reduce light source level from 13 to 12

As part of the original plan for a new lightcurve.

With the old lightcurve lights were so dim all light sources had light
source level 13 or 14 to compensate, resulting in almost no difference
between torchlight and a maximum brightness light.

The new lightcurve makes all light sources effectively much brighter by
spreading visually-bright light further, torches are now slightly too
bright. So now we can reduce the light source level of torches while
actually making them effectively brighter than with the old lightcurve.
This also creates a desirable difference between torchlight and a
maximum-brightness light source.