Make update page labels consistent with topUpdateComp

Summary: Made the labels on the update page consistent with the ones shown in the topUpdateComp of the main window

Test Plan: Check for updates and see that the labels have changed

Reviewers: #discover_software_store, ngraham

Reviewed By: #discover_software_store, ngraham

Subscribers: apol, ngraham, plasma-devel

Tags: #plasma

Differential Revision: https://phabricator.kde.org/D23292