First attempt at implementing adiabatic cooling in macro atoms, not yet ...

...tested

* This adds a destruction probability equal to (cooling_adiabatic / cooling_normalisation)

* if this is the destruction choice, we set photon weight to zero and escape to 1.

This needs fairly rigorous testing, but I am uploading this in a test branch for the moment so others can see and discuss.

Discussion for this issue should go below.