Show warning if own mailbox's API version is incompatible
Show a warning in the mailbox status screen if the API versions supported by our mailbox are incompatible with the versions we support as a client.
The warning could either ask the user to check that Briar and the Mailbox are updated to the latest version, or if we want to be clever we could work out which one needs to be updated and show an appropriate message.
Depends on #2299 (closed)