Add a containment encoding & generalize variablity encodings
- Adds a containment encoding to encode composite structures.
- Use the new containment encoding in the PlatformExploration.
- Add a dedicated structure for subgraphs (directed ones).
- Reduce restrictions for transformation modules such that transformers can produce other artifacts than SuperSets in the transformation process.
Signed-off-by: Alexander Diewald diewald@fortiss.org