core (client): added feedback and sendMessage methods: - feedback method is a helper method to quickly display an info message to user - sendMessage is the method used to send a message in the stream, using message data dictionary. It inclure a trigger point which can't be cancelled, it is intended for e2e encryption method which don't do full stanza encryption. - "send" trigger point is disabled as it is not used at the moment

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