Doxygen for documentation and visualization

[StefanP.MUC]

I just installed a local copy of doxygen+graphviz to generate an overview of the whole sourcecode including visualization graphs (to get a better overview of how the game works). This could also help extremly to create logical and semantic code. I attached an example output of a class inherit graph. That doesn't look to nice yet. The goal should be to create real trees (single root and not-overlapping branches).

I think we should put a git-coupled doxygen on the website somewhere, it'll very much help new devs to see the "who is who" in the source code and the old devs to spot inconsitencies and not-yet-documented code.