Sign then Encrypt

Just as a heads up this is wacky as shit because of some weird merging and rebasing…I'm still looking at it but if you see anything odd please let me know.
@taoeffect, @hoffmabc As it is, the PR is incomplete. Once the message is decrypted and the sig is verified, the recipient should check the `guid` field to verify he is indeed the intended recipient and check the `senderGuid` field to verify the signature was made by the sender.