making irgUtil compile as a catkin package

This involves two steps:
- Adding a package.xml in order to have it picked up as a subdirectory
  by catkin
- Extending the top-level CMakeLists.txt file to make it work in a
  catkin workspace as well as in standalone mode

TODO: check/fix the install target and documentation generation
making kn compile as a catkin package

This involves two steps:
- Adding a package.xml in order to have it picked up as a subdirectory
  by catkin
- Extending the top-level CMakeLists.txt file to make it work in a
  catkin workspace as well as in standalone mode

TODO: check/fix the install target and documentation generation