Added Doxygen

Added Doxygen in

• html
• laxtex
• docbook

Will clean up the class Graphoutput after this prerelease.
Maybe migrate some functionality of it into Visualization?

GPUSAT-Visualization

Added several visualization-options in Graphoutput (graphviz, Neo4j) and Visualization (Tree-Decomposition-Visualization 1.1)

Some helper-functions are placed in gpusatutlis.h and are used mostly in Graphoutput.