Show installed and available versions of updates right there on the page

Summary:
Show the installed and available versions of each app and package update on the delegate rather than hidden away.

Depends on D17922

Test Plan:

This will look nicer on distros that aren't Neon dev, where update strings are shorter and more user-readable. :)

Reviewers: apol, Discover Software Store, VDG

Subscribers: plasma-devel

Tags: Plasma

Differential Revision: https://phabricator.kde.org/D17844