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.

[D-BUS Service]
Name=org.salutatoi.SAT
Exec=sat