GitLab

Unify FindOpenCL.cmake files to one location, under cmake_modules.
Other changes to permit building with nvidia opencl on Windows.

Incorporate apple-specific OpenCL include directory from the other FindOpenCL.cmake in the platforms/opencl CMakeLists.txt file.
TODO - in future use only one FindOpenCL.cmake file.

Reorganized platform analysis in NML init method.
Failed attempt to get OPENMM_PLUGIN_DIR working for NML test.

Turn on free energy plugin by default.
Better rule for when to default build OpenMM wrappers.
Several tweaks to advanced vs. non-advanced cmake variables.

So nightly builds can build CUDA and API wrappers when prerequisites are present.
While still being gentle on third party cmake builders.
New cmake_modules directory contains FindCUDA.cmake from cmake 2.8.0, and
Find OpenCL.cmake from platforms/OpenCL directory.