integrate scrypto

Implement client-side encryption of Conversations and Messages via the Scrypto Rails Engine.

There is still work to do, but it's in a functional state right now.

I haven't done anything to federate the "Scrypto::KeyRing" model. I did add it as a link to the "Person" model and it looks like I might need to alter the "xml_attr" values in that file, but I wasn't sure so I decided to hold off until I gathered your advice.