Increase number of Apps you can see at once in list views

Summary:
This patch increases the number of apps that you can see at once in Discover's list views by doing the following:
- Remove long description and only show caption/short description
- Slightly reduce icon size
- Re-arrange things to make everything a bit more compact

Test Plan:
Tested in KDE Neon. Here's a video:
{F5640019}

Reviewers: apol, #discover_software_store

Reviewed By: apol, #discover_software_store

Subscribers: colomar, plasma-devel

Tags: #plasma

Differential Revision: https://phabricator.kde.org/D9833