Fix install problems

- SampleCMakeLists.txt wasn't being installed (now modified to use config rather than module)
- pkgconfig had incorrect library names on Windows
- changed "CMake" install subdirectory to "cmake" on Windows
- simmath headers were going into the wrong directory
- Problems with SimbodyConfig.cmake: didn't work if there was a space in the installation path name; didn't work on Windows if both Release and Debug libraries were available (not sure about other platforms); left spurious "onelib" variable visible to user in CMake GUI.