Fix generation of config-gammaray.h.

Move generation to end of CMakeLists.txt to properly include HAVE_VTK.
It used to work since it was added as define in the object visualizer
CMakeLists.txt.
Support state machine viewer on servers without GraphViz.

Similar to how we managed to pull this off for the ObjectVisualizer,
we now always build a minimal tool with the server part that
does not depend on Graphviz. The Client part is only build when
GraphViz is found and otherwise shows an error message.