Show users what's changed on confirmation screen

Problem/Motivation

Right now, we install a module such as pathauto. If that depends on ctools, ctools will also get installed. It would be nice to inform the user which modules (and at what versions) were installed.

Proposed resolution

We can use event subscribers to package manager's events coupled with ->getPackagesNotInstalled() (or something like that) and ->getPackagesWithUpgrades() (or similar) - Adam tells me methods such as these exist in the PM api. :)

Then, we when we show the user a confirmation message, we can tell them what happened (including updates, like "we installed pathauto 1.5.6 and upgraded ctools from 4.2.32 to 4.3.1").