Summary: Sort the list of installed apps alphabetically, because sorting by rating count doesn't make much sense when you're looking at a list of what you've already got installed. You don't care how popular other people think it is in that case.

Test Plan:
Tested in KDE Neon. Before:
{F5516317}

After:
{F5516318}

[Ark being listed twice was a pre-existing bug, not introduced by this patch]

Reviewers: apol, #discover_software_store

Reviewed By: apol, #discover_software_store

Subscribers: plasma-devel

Tags: #plasma

Differential Revision: https://phabricator.kde.org/D9026