Added the EDEF Reader & Writer from the Pelix ECF Chat project

This file might be moved in a "misc" or "utils" package as it is not a
bundle.
Also, the "edef" module might be merged with "beans".
First implementation of the MQTT discovery provider

Connects to a MQTT server to publish remote services events.
Based on Eclipse Paho Client (ex-Mosquitto client)
Do not log the endpoints ignored due to their framework UID

The MQTT discovery lets the import registry filter the discovered
endpoints. This commit avoids to have a lot of "local UID" traces in the
log.
Added the MQTT discovery to the remote services sample

Uses the Mosquitto test server as MQTT server.