Rather than verifying eachothers keys separately, you now verify the
privacy with your recipient by sharing a single composite number or
QRCode.
This is a breaking change, in coordination with Desktop and Android.
UX
--
Fingeprint is no longer in line with identity key error. Instead you
have the option of going to the full-screen safety number verification
experience.
Overhauled fingerprint design
-----------------------------
* use same modal dismiss button as elsewhere
* remove fingerprint from settings.
* quick slide in animation vs slow fade
* existing was painfully slow
* blur effect is better metaphor for something slide over top
* anyway there was a rendering glitch in the end of fade where
underlying navbar would "snap" out
Also Fixed
----------
Always provide a name string for contact
* Centralize all the nil-checking
* Fall back to "unknown contact"
allow multi-line error messages
// FREEBIE
Also made identity key scanner appear faster. Previously we were
waiting for camera to initialize. Now we do this after the view has
loaded - with a black background, the affect is preferable than
lagging on the transition.
// FREEBIE
