Improve app icon padding on Application page

Summary: Make the padding to the right of the app icon the same as its left padding.

Test Plan:
Tested in KDE Neon. Before:

After:

Reviewers: apol, andreaska, Discover Software Store, VDG, andreask

Reviewed By: apol, Discover Software Store, andreask

Subscribers: plasma-devel

Tags: Plasma

Differential Revision: https://phabricator.kde.org/D10021