CMakeLists: remove unnecessary link_directories, LIBRARY_OUTPUT_PATH
rviz_imu_plugin: install plugin_description.xml
Update CMakeLists.txt

- added missing installation rules for plugin
- fix imu plugin that doesn't work after catkin_make --install --instal-space /my/install/space
Merge pull request #26 from boris-il-forte/hydro

Update CMakeLists.txt (add install rules to rviz_imu_plugin)