1) Add encryption support for the transport layer. This obscures
metadata from the push messaging provider.
2) Better support the direction multiple destination messages is
headed (one unique message per recipient).
1) Added SMS transport support.
2) Keep track of whether a PreKeyBundle message has gotten
a response, and send them as subsequent messages until
one has been received.
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.
