Add OTR support

[6E006B]

It would be nice to support the OTR (Of The Record) protocol [0][1] to ensure better privacy.
We already thought about using the exchanged keys to encrypt the communication, but that would only work with other TeamMeet instances. Therefore it would be nice to support another defined protocol for end-to-end encryption.

[0] http://www.cypherpunks.ca/otr/
[1] https://en.wikipedia.org/wiki/Off-the-Record_Messaging