setting irg_cmake up as a catkin package

This small amount of hackery allows irg_cmake to be used within
a catkin/ros package. - Small fixes to Modules are also required,
though.
fixing up Uitilities to work with catkin

The assert macro is defined by catkin, too. So we skip it.
The doc-target can only be defined once. Adding
extra logic to have a custom target build as a dependency of the
doc target. - @FIXME: Does not seem to be triggered reliably :(
trying to create a single uninstall target

As I never used the "uninstall" target and am not familiar with the machinery,
I'm not too sure it works out of the box like this.