Add end to end Encryption

[DanWin]

When communicating, one currently has to trust the server admin, since messages are stored in plain text on the server. Adding end to end encryption with perfect forward secrecy would allow users to securely communicate, without having to trust the server admin.
Given that this feature will require a browser extension, or JavaScript, it should be an opt-in feature for users so that users who do not wish to allow executing code on their end can continue using the chat without additional encryption. In that case the server side should encrypt non-encrypted incoming messages to recipients that have e2e encryption enabled, while everyone else encrypts messages in their browser before sending the message.