Non-bonded NxN reaction-field kernels

Tests the non-bonded NxN reaction-field kernels (several CPU + GPU versions).
On the CPU the same kernel is used for reaction-field and plain Coulomb.
For the x86 SIMD kernels the combination rule matters: geometric here.
For the x86 SIMD kernels there is optimization for atoms with/without
LJ or charge, therefore this system has a water and united-atom hexane slab.
