[Wiki] Document PROPERTY_KEY_MQTT_USERNAME and PROPERTY_KEY_MQTT_PASSWORD in JavaSettings.md
[Wiki] Document PROPERTY_KEY_MQTT_USERNAME and PROPERTY_KEY_MQTT_PASSWORD in JavaSettings.md

Change-Id: Ib004dfaaee0e1ceb48c9f9a2c311bf0816b0407e

bmwcarit/joynr,bmwcarit/joynr,bmwcarit/joynr,bmwcarit/joynr,bmwcarit/joynr,bmwcarit/joynr,bmwcarit/joynr,bmwcarit/joynr,bmwcarit/joynr