1) Move all the crypto classes from securesms.crypto.
2) Move all the crypto storage from securesms.database.keys
3) Replace the old imported BC code with spongycastle.
1) There is no longer a concept of "verified" or "unverified."
Only "what we saw last time" and "different from last time."
2) Let's eliminate "verify session," since we're all about
identity keys now.
3) Mark manually processed key exchanges as processed.
