When processing a contact sync with embedded identity key verification info, we
were running overlapping async fetch/save operations on the same conversation
model, causing a race that tends to clobber updates to the contact info.
In this change we extend the application-level contact info handler to block on
a subsequent call to the verification handler, which effectively serializes the
fetch/save calls, and relieves the need for the message receiver to trigger a
seperate event concerning the verification info on contact sync messages.
Fixes#1408
// FREEBIE
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