Add "drag down to refresh"

We're having issues lately where the messages in a room aren't rendering. Probably because the objectWillChange publisher(s) are firing at a bad time, so SwiftUI renders the View before the updated data is ready. I suspect this largely happens when a message decrypts. Somehow that change doesn't cause a re-rendering of the View after the change from the sync that brought us the message before it was decrypted.

Anyway, as a sort of band-aid before we get a better fix, it would be nice if the user could drag down to refresh the View.

We need this feature in at least three places

• Group timeline view
• Circle timeline view
• Photo gallery view