This adds set up and reset actions to each of cross-signing and secure backup
that do separate things, rather than mixing concerns together. (It's temporarily
still a bit of lie for backup, as more changes are needed to stop resetting
cross-signing as well.)
This moves the various 4S status diagnostics to the backup panel and out of the
cross-signing panel. The available actions are unchanged as part of this commit,
but they will be updated next.