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.
Not really sure how it's possible for the system to give us an
extra block of data, but it does if both the input and output
buffers are sized the same during the first decrypt. This
fixes things, but I wish I better understood why it was broken.
