Fix CMake Error when calling find_package(...) from other project

Delete prefix property for 'occupancy_grid_utils' library
Rename 'occupancy_grid_utils' library to 'grid_utils_boost_python_exports'
in order to avoid ambiguities (project name)
Merge pull request #2 from Tones29/hydro-devel

Fix CMake Error when calling find_package(...) from other project