GitLab

Turn default to ON for nightly building Cuda FreeEnergy plugin, since it is desired for pyopenmm release.

Accumulation of Born force was incorrect in USE_OUTPUT_BUFFER_PER_WARP block w/ cell coordinates  x != y

Exported some symbols from Cuda plugin, for use by external NML plugin.
  cudaOpenMMInitializeIntegration, gpuSetConstants, CudaPlatform
  (but I couldn't figure out how to export kGenerateRandoms)
Also turned off TestRandomCuda on Windows, since it always fails and makes the dashboard look bad.
Renamed InitializeIntegration method to cudaOpenMMInitializeIntegration, now that symbol is being exported.

Use a consistent (and more accurate) value for electric constant everywhere.  Also cleaned up handling of constants and units in various places.

Mods to get Free energy plugin libs to compile on Windows; still problem w/ kCalculateLocalSoftcoreForces.cu
and hence OpenMMFreeEnergyCuda lib

Redesigned CustomNonbondedForce to eliminate combining rules and allow the expression to directly use parameters for individual particles.

replaced w/ the "KISS" (Keep It Simple Stupid) random number generator implemented in rng.h & rng.cpp

Free energy plugin added
Plugin will not run w/ Obc or GB/VI forces unless line 2004 of gpu.cpp (gpu->sim.totalNonbondOutputBuffers  = 2*gpu->sim.nonbondOutputBuffers;) is commented in -- working on removing this constraint
Also unit tests for GB/VI currently fail