Fix finding JsonCpp on Ubuntu 16.04 by mapping imported target configs.
Fix finding JsonCpp on Ubuntu 16.04 by mapping imported target configs.

16.04 includes the CMake config files, but only for the "None" config,
resulting in a confusing "Not Found" message at build time for any other
consuming build type. Solution is to map compatible configs - should
also improve building on other platforms as well.

OSVR/OSVR-Core,OSVR/OSVR-Core,godbyk/OSVR-Core,OSVR/OSVR-Core,OSVR/OSVR-Core,godbyk/OSVR-Core,godbyk/OSVR-Core,OSVR/OSVR-Core,OSVR/OSVR-Core,godbyk/OSVR-Core,godbyk/OSVR-Core,godbyk/OSVR-Core