GitLab

1) Added DLL export macros to many classes; enough to get tests to compile
2) Cosmetic changes to reduce warnings in Visual Studio:
   a) change many "for (int i ="... to "for (size_t i ="... to avoid unsigned mismatch warnings
   b) included many explicit static_cast<OpenMMReal>() casts to document places where double->float conversion warnings occur

Added INCLUDE(Dart) to OpenMM CMakeLists.txt

Added 'return platform' to registerReferencePlatform() -- VisualStudio complained about no return value
Added #include "../sfmt/SFMT.h" to SimTKOpenMMUtilities.h to get 'uint32_t' declaration

Continuing to implement ReferencePlatform (implemented GBSA kernels, added test case for SHAKE and fixed some bugs in it)

Continuing to implement ReferencePlatform (implemented kinetic energy calculation and LangevinIntegrator)