Mark headings for semantics in inbox and recipient headers #1964
Description
This was found in #535 (comment) when investigating the app's behavior with a screen reader:
Headers should be marked as such. This includes recipient headers in the message list and the collapsible channel headings on the inbox page. This is probably quite important for the inbox page, since there can be difficulty telling channel and topic items apart.
We should fix this.
A required part of any PR to address this issue will be to try it out with a screen reader and confirm how it behaves. See the description of #535 for instructions.