Improve self-hosted user list for screenreaders

[nbradbury]

As mentioned here, the new self-hosted user list could use some accessibility improvements:

From my perspective, the screen reader experience for this new list could be improved. E.g., swiping up/down moves between individual user items, but merely announces "list" repeatedly, which provides little context.

We might improve the experience by having the top level list declare the total number of items ("list, 25 of 35 users"), individual items could announce some high-level information ("dcalhoun, administrator"), etc.

[dangermattic]

Thanks for reporting! 👍