fixed nbnxn AVX-256 Ewald table pointer alignment

This could lead to access violations, but up till now
this was only observed with 32-bit MSVC builds.
Fixes #1097

Also added more documentation to nbnxn_kernel_simd_utils.h,
renamed macro variables and added minor table optimization
by replacing shuffle with movelh or unpack.

Change-Id: I9df2131cbabb0e6cb86f7224a5fd238acb2e7681
Merge "fixed nbnxn AVX-256 Ewald table pointer alignment" into release-4-6