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

OpenMM/CMakeLists.txt, to probably help build when invoked from
directory above.

Perhaps this will help nightly builds.

2) Began experimenting with attaching actions to Simulate button

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

Modified the initialization order of ForceImpls to prevent them from trying to initialize themselves before the Platform had been chosen