Pomegranate is set to optional but is required

[MalteOlle]

pomegranate is set to optional in pyproject but it is contained in gaitmap/base.py

Ideas for solution:

• try-catch the import
• move import to the places where it is needed
• make pomegranate non-optional

@AKuederle: what would you prefer and do you have any other suggestion?

[AKuederle]

Aah... mist I forgot about this... This is actually a little tricky, because we import it there to allow for json-serialization. I will think about how to handle that best