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:
{F6514892, size=full}

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