Fix discussion list slide gestures on non-mobile touch screens (e.g. iPad)

Touch gestures are enabled on all touch screens, but they are only styled properly on smaller screen sizes. So if you swipe a discussion on iPad, funky stuff happens :O

Start by reproducing the discussion-list swipe gesture on an iPad or other non-mobile touch screen, then trace where touch gestures and small-screen styling are applied. Done means swiping a discussion on larger touch screens behaves and appears correctly without the reported visual issues; no file or test is named in the issue.

Written by the indexing model from the issue text.