GUI: Added initial support for "slider" style buttons. They don't do anything yet.
Added support for parameter parsing to cleandot program.
Integrated GUI "slider" for graph detail levels and controlling abbreviations.

In principle, this is working fine now, except that there are still some
cases where the rendering breaks and we fall back on the original graph.
That's typically very ugly, but at the moment, I don't have a good
solution.