CMakeLists.txt: fix install command (install libs, install includes to corrrect position as well as hxx

[k-okada]

version 0.2.0 did not include any lib/include files...

$ dpkg -L ros-melodic-openslam-gmapping
/.
/opt
/opt/ros
/opt/ros/melodic
/opt/ros/melodic/lib
/opt/ros/melodic/lib/pkgconfig
/opt/ros/melodic/lib/pkgconfig/openslam_gmapping.pc
/opt/ros/melodic/share
/opt/ros/melodic/share/openslam_gmapping
/opt/ros/melodic/share/openslam_gmapping/cmake
/opt/ros/melodic/share/openslam_gmapping/cmake/openslam_gmappingConfig-version.cmake
/opt/ros/melodic/share/openslam_gmapping/cmake/openslam_gmappingConfig.cmake
/opt/ros/melodic/share/openslam_gmapping/package.xml
/usr
/usr/share
/usr/share/doc
/usr/share/doc/ros-melodic-openslam-gmapping
/usr/share/doc/ros-melodic-openslam-gmapping/changelog.Debian.gz