Add ability to have ephemeral chats

[NullVoxPopuli]

Useful for needing to transfer sensitive information (SSN, etc) to someone who you don't care if they have an account -- could expire, you could delete messages, set an expiration on the messages so they'll self-delete, or self-delete upon close of window, etc.

Notes:

• generate ephemeral public/private keys
• give link to person
• person enters name
• you are presented with name, and are asked to allow/deny
• chat connects