Fixed groupSitee indexing, added anotehr device sync, included some (commented) printf lines for debugging

This reverts commit c6c19c64, reversing
changes made to c195bf09.

Added profileStart to GrandBrownTown.cu and allowed nccl_broadcast to overlap with computeForce on GPU 0

Preliminary implementation of multi-gpu communication for nonbonded force calculation; energy kernel not yet implemented

Don't use warp aggregated intrinsics; the compiler for cuda9 and on can do a better job\n\nMaybe older versions of cuda would also perform better