Keep SAM enabled when switching images

[dlangenk]

Usually when changing the image the current annotation mode is not disabled. However, when SAM is enabled and I change the image I always have to reactive it. I guess this is because of the computation of embeddings, but it would be much more convenient when it would automatically be enabled, especially when the embeddings are already present for a whole volume (cmp. #5).

[mzur]

I'm not sure if there was another reason for this than that it was easier to implement this way. You are right that this should be consistent with the other annotation tools.