OMEMO encryption for XMPP

[butyoutried]

Please add support for XEP-0384.

These plugins for libpurple may be useful: lurch and libpurple-omemo-plugin (development is stalled).

See also: https://conversations.im/omemo/

[JadedCtrl]

https://github.com/dino/libomemo-c looks like a useful library for adding OMEMO support to the native XMPP add-on, it looks like https://github.com/dino/dino uses it.

[Neustradamus]

@JadedCtrl: In more libomemo-c, there is picomemo:

• https://github.com/mierenhoop/picomemo