Aptitude mixed-install/apt-pinning integration

A simple preferences file editor of course is not enough. We would like a good visualization of how each pinning rule changes the packages version choices in the resolver. This can mean particular highlighting in the versions list of a package or specific views explaining which specific set of packages (coming from the same source package for example, or depending on a specific package, etc.) is subject to an apt-pinning exception.

The goal here is to give a clear view to the user of what is going on on a debian install which may have multiple distributions, or unofficial archives with packages that already exist in main (backports, debian-multimedia, winehq, developer personal repositories, ... ubuntu PPAs). This is particularly useful to power users and developers.