1153 Add content_guessing optional param to imports API

@Kartones can you please review?
I'm with Kartones on this. I think all dependencies should be explicit. In the mid term I think we should refactor logging to a single class, both debug info and exception reporting, since I think it's the same responsibility (reporting what's going on) even if different levels lead to different effects. Certainly having many parameters in constructors is a smell, but that should not mislead us to using globals but to more refactor. In the short term, until we can reduce complexity, I think having too many explicit dependencies is less harmful than having hidden ones. For example, it allows unit testing.