irg_cmake catkin package

Hi Mark,

these changes basically allow irg_cmake to also be used as a catkin package.
The patches to the Setup files are more like a proof of concept.
I didn't get to test them yet in the roversw setup.

To the assert macro I added some conditional compilation logic, which is simple enough to work.
For the doc & uninstall targets I tried to add logic to create dependent targets. - I'm not sure if that's the recommended way of doing it or what other side-effects need to be taken care of.