Implementing adiabatic cooling as kpkt destruction choice

This change implements adiabatic cooling as a kpkt destruction choice so it works in macro atom mode.

This involves:
* Adding a destruction choice in kpkt(), with a probability proportional to the adiabatic_cooling in that cell, normalise by the total cooling
* this destruction choice sets photon weight to zero
* also modifies istat to new definition P_ADIABATIC, which breaks loop in trans_phot()

Testing in progress.