Allow specifying packages are successors / incompatible

**Describe the feature request**
Recently I forked the memory package as ram. This to end the basement/baseplate discussion by just ripping out basement from memory and other packages.

Now downstream users may get really bad error messages if they upgrade (crypton) for example. A type used from memory is incompatible with a type used from ram.
What I would like is to inform users that if the solver pulls in both memory and ram, something is going wrong. Instead of random compile or constraint errors.

This should make the community a bit more resilient against contactable but hostile maintainers.

**Additional context**
I decided to split it in this discussion: https://discourse.haskell.org/t/fork-basement-as-baseplate/12415/64