Make it easier to distinguish between replying and writing a new post in a forum or private group
In a recent testing session we noticed that it was easy to accidentally write a top-level post in a forum or private group when intending to reply to another post.
Some things that might help:
- Increase the visual difference between the "replying" state and the "writing a new post" state (eg look at what Signal does)
- Increase the size of the reply button so it's easier to hit
- Allow a reply to be started by right-swiping a post
Related to #1948, as we currently use the same highlighting for the post being replied to as we use for unread posts.