Vertical split compact view

[Scheirle]

It would be nice to have a (optionally?) vertical split instead of horizontal split for the expanded compact view.
It is of cause quite similar to the default non-compact view, but having 20 vs only 7 unread articles on the screen makes a big difference in my opinion.

Somewhat related requests: #1553 #2895 #94

[Scheirle]

Done with #2950 (released with 25.1.0). Thank you.