Generate various diagrams in the C# plugin

[mcserep]

The C# plugin should be able to produce similar diagrams than the C++ plugin.
Some examples: function call diagram, class diagramm, dependency diagrams (file and directory level), CodeBites.

These should be the same interactive Graphviz SVG diagrams as they exist for the C++ plugin to have a unified approach for diagrams.

Some initial work has been done on the csharp_diagrams branch of @intjftw's fork, which should be checked and reuse the existing approach and parts if possible:
https://github.com/intjftw/CodeCompass/commits/csharp_diagrams/

Code changes can be tracked here:
intjftw#1