Provide additional rendering algorithms besides GraphViz

[StephanPirnbaum]

ContextMapper requires GraphViz for rendering the context maps.
This can be difficult in a corporate environment both on the local developer pc due to missing admin rights as well as on the build server as often additional libraries are not allowed to be installed.

PlantUML, therefore, provides additional options with Smetana and Elk for rendering the diagrams. Especially Elk gives optically pleasent visualizations.

Is this something you could imagine having in ContextMapper also?

[stefan-ka]

Very good input, thanks @StephanPirnbaum.
I know the graphviz dependency is sometimes a bit cumbersome. We should definitely have a look into this, thanks!