core (memory/encryption): set encrypted flag also for outgoing messages and put it in extra: - `encrypted` flag is now put directly in extra, so that there is nothing to change when sending the message to bridge for frontends to be aware of it. - this flag is now also set when markAsEncrypted is used, so frontend can display appropriate indicator to show that outgoing message is encrypted or not.

You'll find install instructions in documentation (see doc/installation.rst).

If you need help, come the SàT official XMPP room: sat@chat.jabberfr.org or join us with a web browser via https://chat.jabberfr.org/converse.js/sat@chat.jabberfr.org