Forward secure encrypted channel

[schulze]

For different reasons, but mostly for simplicity, Qabel's standard encrypted channel is not forward secure. For special applications, e.g. chat clients, we could/should add the possibility to have forward secure sessions. If these are not synchronised cross device, this would simplify the design considerably.

There are numerous possibilities ranging from using noise's pipes, OTR, or an axolotl based protocol (TextSecure) to maybe an multi-party OTR protocol (if one materialises in time).

(Cf. #73 for some of the past discussion.)