Add new Combination method that takes the Boltzmann mean of the pose predictions, ie

$$\Delta \mathrm{G} = \sum w_n \Delta \mathrm{G}_n$$

where

$$w_n = \frac{\mathrm{exp} \left( -\Delta \mathrm{G}_n \right)}{\sum_{i=1}^N \mathrm{exp} (-\Delta \mathrm{G}_i )}$$