[EXTERNAL] Compute elastic constant tensor for a crystal

Elastic constants at temperature can be calculated in the same manner as the zero temperature ELASTIC script. However, while the ELASTIC script has essentially only 1 convergence parameter, the strain magnitude {up}, at temperature there are quite a few more: equilibration time, stress sampling time, stress sampling frequency, MD timestep. Also these interact strongly with {up}. This makes it hard to reduce it down to a black box.