UX: fix layout of group header buttons on mobile (PR #12781)

I also moved the message button to consistently be on the right and made sure these wrap well with longer translations.

Before:

Screen Shot 2021-04-21 at 12 00 16 AM

After:

Screen Shot 2021-04-21 at 12 02 39 AM

GitHub

The title of this pull request changed from “Group–header buttons” to "UX: fix layout of group header buttons on mobile

This pull request has been mentioned on Discourse Meta. There might be relevant details there: