Refactoring of the nonbonded free energy kernel to enable easier...

Refactoring of the nonbonded free energy kernel to enable easier implementation of new soft-core potentials.

To this end, the soft-core potential is now represented by a SoftcoreCalculator class implementing a potential-specific version of the old nb_free_energy_kernel. The new NBFreeEnergyKernel consists of a structure used to initiate the kernel-specific variables and 11 sub-functions. Of these, seven are independent of the type of soft-core potential used and gathered in a shared base class to be used by all kinds of SoftcoreCalculator. Moreover, the dispatchKernel functions are now templated on SoftcoreCalculator.