Rewrote findBlocksWithInteractions() in a way that is both faster and simpler.
Ported the new version of findBlocksWithInteractions() to OpenCL (not yet debugged)
Bug fixes
Improved performance of building neighbor list on AMD GPUs
Fixed bug on Intel GPUs
Cleaned up obsolete code
Merge pull request #609 from peastman/nb

Rewrote the neighbor list generation kernel to be simpler and (slightly) faster