Swipe gesture on mobile

[nolanlawson]

Swipe left and right on a timeline to switch columns, so you don't need to tap the button in the navigation header.

I avoided this because I found that the react-swipeable-views on Mastodon sometimes has false positives on certain browsers. E.g. on mobile Firefox you scroll down, but it's interpreted as a swipe, which is confusing. Also touchmove events can block scrolling.

I think it may be possible to do this performantly and accurately with Pointer Events, but this needs some investigation first.

[nolanlawson]

Update: I would be willing to do this if

1. It used pointer events rather than touch events so that scrolling is not de-optimized
2. It had good heuristics to avoid false positives
3. It had an option to disable it

We could also make the keyboard shortcuts <- and -> go left and right.