Support gamma + A?

[HDembinski]

In the SFB Leptohadronic workshop, I learned about the importance of gamma+p and gamma+A interactions for this community.

• Do we have models which support gamma + A?
• Can we enable this process in some models, where the model supports it but our interface does not?
• A function in chromo.utils would be useful which returns a list of models that support a given input state. The function can use the public interface of each model to check whether projectile and target are supported.