Initial content for card

Summary:
Merge branch 'master' into card

Added recomendation for aspect ratio

Add3d remoendation for padding to card

added 2 images for cards

Added recomendation about focus on one bit of content to cards

Merge branch 'master' into card

Reviewers: mart, VDG

Reviewed By: mart

Subscribers: colomar

Tags: KDE Human Interface Guidelines

Differential Revision: https://phabricator.kde.org/D13340