convert XTRA to use components compiled by Native_component_list
convert SIDE_CHAIN to use components compiled by Native_component_list
convert NB to use components compiled by Native_component_list
correct bad exception message (parameters swapped)
convert NB to use components compiled by Native_component_list
finish move to compiled components for ATOM comp't in force calculators
move calc_shifts to base class (Base_potential)
convert DIHEDRAL shifts to use Native_component_list compiled components
convert distance based shifts to use compiled components

specifically NON_BONDED, XTRA, SIDE_CHAIN, BACK_BONE