Support MQTT authentication

Author: davidlb

plugin.py

@@ -9,6 +9,8 @@
     <params>
         <param field="Address" label="MQTT Server address" width="300px" required="true" default="127.0.0.1"/>
         <param field="Port" label="Port" width="300px" required="true" default="1883"/>
+        <param field="Username" label="MQTT Username" width="300px" required="false" default=""/>
+        <param field="Password" label="MQTT Password" width="300px" required="false" default=""/>
         <param field="Mode1" label="Zigbee2Mqtt Topic" width="300px" required="true" default="zigbee2mqtt"/>
         <param field="Mode2" label="Zigbee pairing" width="75px" required="true">
             <options>
@@ -191,4 +193,4 @@ def onCommand(Unit, Command, Level, Color):
 
 def onHeartbeat():
     global _plugin
-    _plugin.onHeartbeat()
+    _plugin.onHeartbeat()