Add plot function for debugging DAG of transformation framework

This MR adds visualisation of the DAGs and several other improvements, e.g. Transformation.context and Transformation.layer ...

A DAG visualisation can look like this:

The visualisation helps in understanding what kind of transformations will occur and can be very helpful for debugging.

Can this MR be accepted?

• Implementation ready
• Tests added or adjusted
• Documentation extended or updated

• Code quality
  • Changes follow coding guidelines
  • Checked code coverage on new and adjusted code

• Ready for merging
  • Pipeline passes without warnings
  • History cleaned-up or squash option set
  • Changelog entry added
  • Version number bumped
  • Reviewed & approved

Related issues

Closes #258 (closed)