Extract dependencies by tree walking

_This is a preview of a PR that is coming soon. It's not finished yet but I decided to send it so I can get @harrah's feedback early_

This PR introduces new `memberRef` and `inheritance` relations. Also, the logic that populates those relations by tree walking is provided.

I'd love to hear if this is going in the right direction. Most of commit messages has been updated so they are up-to-date with patches I submit here. They could help with answering some of the questions that might arise during the review.