When resolving conflicts, we should not only discard the old key, but
set the new trusted key to the one the user has verified. Previously, we
would end up trusting the first-seen new key, which may not be the one
the user verified.
// FREEBIE
Clicking on a key conflict message opens the message detail view,
which displays the contact(s) in this conversation. If the message
contains a key conflict with any of these contacts, a button is
displayed which attempts to resolve that conflict and any other
conflicts in the conversation that are related to that contact.
