Adding a CMake config

This enables finding and linking against the library with the preferred
CMake mechanism (as opposed to piggybacking on pkgconfig). The absolute path to the library enables multiple installations side-by-side, you can point CMake to the one you want to use with the env.var `sbpl_DIR`.

With this I am able to use a source installation of SBPL in top of a binary release in ROS (hydro and catkin), otherwise you need to completely uninstall the SBPL package (and all depending libraries) so that only one include a linking path is found.