Add templating for NbnxnPairlistGpu and nbnxn_cj_packed_t

No functionality changes, merely templating of these classes. The only instantiations of each makes an object that is identical to the previous version.

Manually inlined three related functions that would otherwise have needed templating. The fucntion names were more confusing than the variable name that is now used to describe the inlined operation.

Made other minor related changes necessary to compile.

Also made some related function and variable usage conform to style.

Refs #3847